United States Office of Water Regulations EPA 440/1 -85/061 -B
Environmental Protection and Standards (WH-552) October 1985
Agency Washington, DC 20460
Water
Development
Document for Proposed
Effluent Limitations
Guidelines and
New Source Performance
Standards for the
Ore Mining and Dressing
Point Source Category
Gold Placer Mine
Subcategory
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Development Document
for Proposed
Effluent Limitations Guidelines and
New Source Performance Standards
for the
Ore Mining and Dressing Point Source Category
Gold Placer Mine Subcategory
Lee M. Thomas
Administrator
Lawrence J. Jensen
Assistant Administrator for Water
Edwin L. Johnson
Director
Water Regulations and Standards
Jeffery D. Denit
Director, Industrial Technology Division
Baldwin M. Jarrett
Project Officer
October 1985
Industrial Technology Division
Office of Water
U. S. Environmental Protection Agency
Washington, D. C. 20460
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Table of Contents
Section Page
I Executive Summary
Summary of Recommended Limitations
and Standards 1-4
Best Practicable Technology 1-5
Best Conventional Technology 1-6
Best Available Technology 1-8
New Source Performance Standards 1-9
II Introduction
Purpose II-l
Legal Authority II-2
Prior EPA Regulations II-9
History of Regulation of Gold
Placer Mines 11-11
Industry Overview 11-18
General Approach and Methodology 11-22
III Industry Profile
Historical Perspective III-l
Description of the Industry III-4
Mining Methods 111-12
Processing Methods 111-24
Industry Practice 111-35
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Table of Contents (continued)
Section Page
IV Industry Subcategorization
Technical Considerations
Influencing Subcategorization IV-2
Subcategorization Based on
Technical Consideration IV-18
Economic Considerations IV-18
Proposed Subcategorization for Gold
Placer Mines IV-20
V Sampling and Analysis Methods
Sampling and Analysis Programs V-l
Site Selection and Reconnaissance
Study V-3
Sample Collection, Preservation,
and Transporation V-9
VI Wastewater Characterization
Reconnaissance Data VI-1
Treatability Analysis VI-3
Correlations of Total Suspended
Solids (TSS) with Arsenic (As)
and Mercury (Hg) VI-5
Appendix VI-1
Statistical Methodology VI-1-1
Appendix VI-2
Listing of Effluent Pollutant
Values VI-2-1
Appendix VI-3
Correlations of TSS with As and
Hg VI-3-1
IV
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Table of Contents (continued)
Section
Page
VII
VIII
IX
Appendix VI-4
Summary of Flocculant Aided
Settling
Selection of Pollutant Parameters
Settlement Agreement, Natural
Resources Defense Council v_^
Train
Data Base
Selected Pollutant Parameters
Exclusion of Toxic Pollutants
Surrogate/Indicator Relationships
Control and Treatment Technology
In-Process Control Technology
End-of-Pipe Treatment Technology
Treatment System Options
Historical Data Summary
Best Management Practices
Cost, Energy, and Other Non-Water
Quality Issues
Development of Cost Data Base
Capital Cost of Facilities
Annual Cost
Treatment Process Costs
Sample of Cost Estimating for
Placer Mine Site
Treatment Costs for Options
Treatment Costs for Model Mines
VI-4-1
VII-1
VII-2
VII-4
VII-5
VII-13
VIII-1
VIII-4
VIII-19
VIII-21
VIII-34
IX-1
IX-2
IX-5
IX-7
IX-14
IX-20
IX-22
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Table of Contents (continued)
Sect ion Page
X Best Practicable Technology (BPT)
Technologies Considered X-3
Specialized Definitions for Gold
Placer Mines X-6
Summary of Proposed BPT Effluent
Limitations Guidelines X-9
Specialized Provisions for Gold
Placer Mines X-15
Guidance for Implementing the
Specialized Provisions for
Gold Placer Mines X-19
Storm exemption X-19
Mine drainage X-24
Process capacity X-27
XI Best Conventional Pollutant Control
Technology (BCT)
Technologies Considered XI-1
BCT Cost Test XI-6
XII Best Available Technology Economically
Achievable (BAT)
NRDC Settlement Agreement XII-3
Engineering Aspects of BAT XII-8
XIII New Source Performance Standards (NSPS)
XIV Pretreatment Standards
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SECTION I
EXECUTIVE SUMMARY
This development document presents the technical data base
developed by EPA to support effluent limitations guidelines and
standards for the Gold Placer Mine Subcategory of the Ore Mining
and Dressing Point Source Category. The Clean Water Act of 1977
sets forth various levels of technology to achieve these
limitations: best practicable technology (BPT), best available
technology economically achievable (BAT), best conventional
pollutant control technology (BCT), and best available
demonstrated technology (BADT). Effluent limitations guidelines
based on the application of BPT, BAT, and BCT are to be achieved
by existing sources. New source performance standards (NSPS)
based on BADT are to be achieved by new facilities. These
effluent limitations guidelines and standards are required by
Sections 301, 304, 306, 307, and 501 of the Clean Water Act of
1977 (P.L. 95-217). They augment the regulations promulgated on
December 3, 1982 for other subcategories of the ore mining
industry.
The Act included a timetable for issuing these standards.
However, EPA was unable to meet many of the deadlines and, as a
result, in 1976, it was sued by several environmental groups. In
settling this lawsuit, EPA and the plaintiffs executed a
"Settlement Agreement" which was approved by the court. This
Agreement required EPA to develop a program and adhere to a
schedule in promulgating effluent limitations guidelines, new
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source performance standards, and pretreatment standards for 65
"priority" pollutants and classes of pollutants for 21 major
industries, including the Ore Mining and Dressing industry. See
Natural Resources Defense Council, Inc. v. Train, 8 ERC 2120
(D.D.C. 1976), modified, 12 ERC 1833 (D.D.C. 1979), modified by
Orders dated October 26, 1982, August 2, 1983, January 6, 1984,
July 5, 1984, and January 7, 1985. Many of the basis elements of
the Settlement Agreement were incorporated into the Clean Water
Act of 1977. Like the Agreement, the Act stressed control of
toxic pollutants, including the 65 "priority" pollutants and
classes of pollutants.
At present there are over 600 commercial gold placer mines which
are active in a given mining season (total operations including
recreational and assessment mines may number over 1000) in the
United States. Approximately two-thirds of these mines are
located in Alaska. All existing gold placer mines are point
sources and direct dischargers; there are no known existing
indirect dischargers and no new source indirect dischargers are
anticipated. (Indirect dischargers are those facilities which
discharge to a publicly owned treatment works or "POTW".)
Consequently, pretreatment standards, which control the level of
pollutants which may be discharged from an industrial plant to a
publicly owned treatment works, are not included in this
proposal.
To recognize inherent differences in the ore mining industrial
category, EPA established subcategories within the larger
category. The 1982 regulation for the ore mining and milling
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industry was divided into 11 major subcategories based upon metal
ore and 27 subdivisions based upon whether the discharge was from
a mine or mill, and then further based upon the process employed
at the mill. Included in the subcategory for gold ores is a
subdivision for gold placer mines which reserved effluent
limitations and standards for these mines because EPA did not
have sufficient technical or economic data to develop appropriate
regulations.
An extensive sampling and analysis effort was undertaken in 1983
and 1984 and extends to the present. As part of this effort, 68
placer mines were visited for screening and wastewater sampling.
Of these 68 mines, 26 were visited two or more times for
verification sampling, and 21 treatability studies were performed
at 19 of these mines, Also, data collected by EPA Regions VI,
VIII, IX and X were reviewed. Twenty-nine of the mines visited
also provided cost and operating information. Studies were
performed by EPA on gold recovery using recycle water with high
TSS concentrations in a sluice. Similar data and information
were supplied by Alaska Department of Environmental Conservation.
The data base also includes National Pollutant Discharge
Elimination System (NPDES) discharge monitoring reports (DMR's)
and other data submitted by the industry.
Two studies have been performed to determine the cost of
implementation of the various control technologies considered.
The first exercise determined the cost of technologies based on
model (typical) mines. The second costs the technologies in 1984
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dollars based on data from approximately 11 placer mines for
which we have information from an economic survey.
Subcategorization of the Gold Placer Mine Industry
EPA is proposing to remove gold placer mines from the subcategory
promulgated for all gold ores, i.e., hard rock ores, and
establish a separate subcategory specifically for gold placer
mines because gold placer mines and the recovery of gold from
placer deposits uses different mining and processing methods. EPA
has also determined that based on technical and economic
considerations, separate effluent limitations guidelines and
standards are appropriate for various groups of placer mines
based on the mining method and the mine's size or process
capacity. Accordingly, the Agency has further subdivided the
industry into non-commercial mines, e.g., small mines including
recreational and assessment mines (<20 yd^/day of paydirt),
which are not included in this regulation and commercial mines
(>20 yd3/day). Commercial mines are further subdivided by
mining method into large dredges (>4000 yd^/day) and all
other mining methods. The costs to implement technology
developed in this document when applied to the economic models
indicates that small commercial mines with a capacity of 20 to
500 yd^/day are often marginally profitable. Therefore, EPA
is proposing separate limitations for these mines with this
capacity (all mining methods) and mines over 500 yd^/day (all
mining methods).
Summary of the Recommended Limitations and Standards
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The effluent limitations and standards proposed in this document
are intended to control the discharge of process wastewater from
the gold recovery process. However, other wastewater, including
mine surface drainage, seepage, and ground-water infiltration
into existing settling ponds, is often commingled, treated, and
discharged. Under this proposed regulation, these combined waste
streams would have to meet certain effluent limitations and
standards, i.e., those that apply to process wastewater from
operations processing 20-500 yd3/day (all mining methods).
For facilities required to meet a no discharge of process
wastewater requirement, the volume of water that may be
discharged under this provision cannot include the volume of
water subject to the no discharge standard.
This regulation also proposes a storm exemption when there is
excessive precipitation, under certain conditions, i.e., the
treatment system was designed, constructed, and operated to
contain or treat the volume or flow that would result from a 5-
year, 6-hour rainfall plus the normal volume or flow from the
gold recovery process. Because of pond design and site
differences, the design condition is based on a 5-year, 6-hour
rainfall rather than the 10-year, 24-hour rainfall available to
the rest of the ore industry.
Best Practicable Technology (BPT)
The factors considered in defining BPT include the total cost of
application of BPT in relation to the effluent reduction
benefits. In general, BPT represents the average of the best
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existing performance of operations with common characteristics
and focuses on end-of-pipe treatment rather than process
controls. Four effluent control technologies were considered for
BPT: (1) simple settling, (2) simple settling with 80 percent
recycle, (3) flocculant addition to the blowdown from 80 percent
recycle, and (4) 100 percent recycle of process water used in
gold recovery. While the 1977 date for compliance with BPT, has
passed, BPT is being proposed because existing treatment at many
placer mines is inadequate to establish a baseline for treatment.
BPT for all commercial mines larger than 20 yd^/day, except
large dredges, is based on simple settling (Option 1) to achieve
0.2 ml/1 settleable solids and 2000 mg/1 TSS in the effluent.
BPT for large dredges is based on recycle of process water from
the pond used to float the dredge (Option 4) to achieve no
discharge of process wastewater. The provision for commingled
water and the storm exemption described above would both apply.
Best Conventional Pollutant Control Technology (BCT)
BCT replaces BAT for control of the conventional pollutants:
total suspended solids (TSS), pH, biochemical oxygen demand
(BOD), oil and grease (O&G), and fecal coliform. Fecal coliform,
BOD, and O&G were not found in significant concentrations above
background of the intake water at gold placer mines,. The pH of
the discharges was also about the same as the pH of the intake
water, approximately neutral. However, solids in the wastewater
discharges from gold placer mines have long been identified as
the major pollutant in placer mine discharges. TSS, a
conventional pollutant, is the parameter which measures solids.
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The same four technologies considered for BPT were considered for
BCT. The Act requires BCT limitations to be considered in light
of the cost to implement the technology to obtain the limitations
when compared to costs at publicly owned treatment works to
obtain similar levels and the cost-effectiveness of treatment
beyond BPT. The "cost reasonableness" of each technology was
determined for each subcategory based on the cost per pound of
solids, e.g., TSS, removed. BCT for small commercial mines (20
to 500 yd3/day) is proposed equal to BPT (2000 mg/1 for TSS)
because of the potential cost effects on this group of more
stringent requirements. BCT for large commercial mines (over 500
yd^/day) including large dredges is proposed as no discharge
of process wastewater. BPT for large dredges is already proposed
as no discharge and no more stringent technology to control TSS
could be identified, so BPT = BCT for this segment. The cost of
solids removed by total recycle of process wastewater (no
discharge of process wastewater) at commercial mines processing
more than 500 yd3/day is less than 4 mils per pound of
solids. Although EPA has not promulgated a "cost-reasonableness"
BCT methodology, this cost is sufficiently low to pass any test
that may be promulgated. Recycle technology at 100 percent is in
use at some large commercial mines and is available to the other
mines as a process change without loss of recoverable gold based
on pilot tests conducted.
As in BPT, the net volume of mine drainage and infiltration
groundwater may be discharged subject to limitations on TSS (2000
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mg/1). The storm exemptions for relief from precipitation also
apply.
BEST AVAILABLE TECHNOLOGY ECONOMICALLY ACHIEVABLE (BAT)
The presence or absence of the 126 toxic pollutants and a
nonconventional pollutant, e.g., settleable solids, was
determined, in EPA's sampling and analysis program. All 126
toxic pollutants have been excluded from regulation in the gold
placer mine subcategory based upon one of the criteria contained
in the Settlement Agreement cited previously: (1) they were not
detected, (2) they were present at levels not treatable by known
technologies, or (3) they were effectively controlled by
technologies upon which other effluent limitations are based.
Two toxic pollutants, arsenic and mercury, were identified in
treatable amounts in the discharges from placer mines. However,
EPA is not proposing limitations for these pollutants because EPA
believes they will be adequately controlled by BCT limitations on
TSS and BAT limitations on settleable solids. Therefore, for
small commercial mines (20 to 500 yd^/day), BPT = BCT = BAT.
More stringent limitations for small commercial mines are not
proposed because the costs identified in this document are not
economically achievable. For large commercial mines, (over 500
yd3/day) including large dredges, EPA is proposing no
discharge of process wastewater, BCT = BAT; no more stringent
technology upon which to base limitations has been identified.
The commingled wastewater provision and storm exemption
described above would be available at BAT.
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NEW SOURCE PERFORMANCE STANDARDS (NSPS)
New facilities have an opportunity to implement the best and most
efficient ore mining and milling processes and wastewater
treatment technologies. Accordingly, Congress directed EPA to
consider the best demonstrated process changes and end-of-pipe
treatment technologies capable of reducing pollution to the
maximum extent feasible through a standard of performance which
includes, "where practicable, a standard permitting zero
discharge of pollutants."
Standards for new source gold placer mines are proposed based on
the same technology proposed for BCT and BAT. The same general
characteristics of wastewater, costs to treat, and percentages of
pollutant removals are expected in new sources as found in
existing sources. New source standards equivalent to existing
source limitations would not pose a barrier to entry.
Solicitation of Comments
This document supports a rulemaking proposed by EPA for
regulating the wastewater discharges from gold placer mines. The
Agency requests comments relating to errors, deficiencies, or
omissions in this document with facts and information that will
correct or supplement the data.
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SECTION II
INTRODUCTION
PURPOSE
In the effluent limitations guidelines and standards for the ore
mining and dressing point source category, the gold placer mining
industry was classified as follows:
Category; Ore Mining and Dressing
Subcategory; Copper, Lead, Zinc, Gold, Silver and Molybdenum
Ores
Subdivision; Mills or Hydrometallurgical Beneficiation
Process; Gravity Separation Methods (Including dredge, placer,
or other physical separation methods; mine drainage or mines and
mills).
During the BPT round of rulemaking (promulgated in 1978) and BAT
rulemaking (promulgated in 1982), the effluent limitations
guidelines for this segment were reserved.
EPA has conducted various studies to determine the presence and
concentrations of toxic (or "priority") pollutants in the waste
water discharged from the gold placer mining segment. This
development document presents the technical data base compiled by
EPA with regard to these pollutants, as well as conventional and
nonconventional pollutants, and evaluates their treatability for
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regulation under the provisions of the Clean Water Act.
This document outlines the technology options considered and the
rationale for the option selected at each technology level.
These technology levels are the basis for the limitations and
standards of the proposed regulations. No pretreatment standards
are proposed, because there are no known indirect dischargers in
this segment, nor are there likely to be, because most operations
are rural and far from any publicly owned treatment works (POTW).
LEGAL AUTHORITY
These regulations are proposed under authority of Sections 301,
304, 306, 307, 308, and 501 of the Clean Water Act (the Federal
Water Pollution Control Act Amendments of 1972, 33 USC 1251 e_t
seq., as amended by the Clean Water Act of 1977, P.L. 95-217)
(the "Act").
The Clean Water Act
The Federal Water Pollution Control Act Amendments of 1972
established a comprehensive program to "restore and maintain the
chemical, physical, and biological integrity of the Nation's
waters," Section 101(a). By 1 July 1977, existing industrial
dischargers were required to achieve "effluent limitations
requiring the application of the best practicable control
technology currently available" (BPT), Section 301(b)(1)(A). By
1 July 1983, these dischargers were required to achieve "effluent
limitations requiring the application of the best available
technology economically achievable . . . which will result in
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reasonable further progress toward the national goal of
eliminating the discharge of all pollutants" (BAT), Section
301(b)(2)(A). New industrial direct dischargers were required to
comply with Section 306 new source performance standards (NSPS),
based on best available demonstrated technology. The
requirements for direct dischargers were to be incorporated into
National Pollutant Discharge Elimination System (NPDES) permits
issued under Section 402 of the Act. Although Section 402(a)(l)
of the 1972 Act authorized the setting of requirements for direct
dischargers on a case-by-case basis, Congress intended that, for
the most part, control requirements would be based on regulations
promulgated by the Administrator of EPA. Section 304(b) of the
Act required the Administrator to promulgate regulations
providing guidelines for effluent limitations setting forth the
degree of effluent reduction attainable through the application
of BPT and BAT. Moreover, Sections 304(c) and 306 of the Act
required promulgation of regulations for designated industry
categories, Section 307(a) of the Act required the Administrator
to promulgate effluent standards applicable to all dischargers of
toxic pollutants. Finally, Section 301(a) of the Act authorized
the Administrator to prescribe any additional regulations
"necessary to carry out his functions" under the Act.
EPA was unable to promulgate many of these regulations by the
dates contained in the Act. In 1976, EPA was sued by several
environmental groups, and in settlement of this lawsuit, EPA and
the plaintiffs executed a settlement agreement that was approved
by the Court. This agreement required EPA to develop a program
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and adhere to a schedule for promulgating for 21 major industries
BAT effluent limitations guidelines and new source performance
standards covering 65 priority pollutants and classes of
pollutants. See Settlement Agreement in Natural Resources
Defense Council, Inc. v^ Train, 8 ERC 2120 (D.D.C. 1976),
modified, 12 ERC 1833 (D.D.C. 1979), modified by Orders of
October 26, 1982, August 2, 1983, January 6, 1984, July 5, 1984,
and January 7, 1985.
On 27 December 1977, the President signed into law the Clean
Water Act of 1977 (P.L. 95-217). Although this act made several
important changes in the federal water pollution control program,
its most significnt feature was its incorporation of several
basic elements of the NRDC Settlement Agreement program for toxic
pollution control. Sections 301(b)(2)(A) and 301(b)(2)(C) of the
Act required the achievement, by 1 July 1984, of effluent
limitations requiring application of BAT for toxic pollutants,
including the 65 priority pollutants and classes of pollutants
that Congress declared toxic under Section 307(a) of the Act.
Likewise, EPA's programs for new source performance standards are
now aimed principally at toxic pollutant controls. Moreover, to
strengthen the toxics control program, Section 304(e) of the Act
authorizes the Administrator to prescribe best management
practices (BMPs) to control the release or toxic and hazardous
pollutants from plant site runoff, spillage or leaks, sludge or
waste disposal, and drainage from raw material storage associated
with, or ancillary to, the manufacturing or treatment process.
This proposed regulation provides effluent limitations guidelines
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for BAT and establish NSPS on the basis of the authority granted
in Sections 301, 304, 306, 307, and 501 of the Clean Water Act.
As explained earlier, pretreatment standards (PSES and PSNS) were
not proposed for the gold mining segment of the ore mining and
dressing point source category, since no known indirect
dischargers exist nor are any known to be in the planning stage.
In general, ore mines and mills, particularly gold placer mines
in Alaska and several other states, are located in rural areas,
far from any POTW.
GENERAL CRITERIA FOR EFFLUENT LIMITATIONS
BPT Effluent Limitations
The factors considered in defining BPT include the total cost of
applying such technology in relation to the effluent reductions
derived from such application, the age of equipment and
facilities involved, the process employed, nonwater quality
environmental impacts (including energy requirements), and other
factors the Administrator considers appropriate [Section
304(b)(1)(B)]. In general, the BPT technology level represents
the average of the best existing performances of plants of
various ages, sizes, processes, or other common characteristics.
Where existing performance is uniformly inadequate, BPT may be
transferred from a different subcategory or category. BPT
focuses on end-of-pipe treatment rather than process changes or
internal controls, except where the latter are common industry
practice. The cost/benefit inquiry for BPT is a limited
balancing, committed to EPA's discretion, which does not requre
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the Agency to quantify benefits in monetary terms. See, e.g.,
American Iron and Steel Institute y_^ EPA, 526 F.2d 1027 (3rd Cir.
1975). In balancing costs in relation to effluent reduction
benefits, EPA considers the volume and nature of discharges
expected after application of BPT, the general environmental
effects of the pollutants, and the cost and economic impacts of
the required pollution control level. The Act does not require
or permit consideration of water quality problems attributable to
particular point sources or industries, or water quality
improvements in particular water bodies. Therefore, EPA has not
considered these factors. See Weyerhaejjser Co. y_^ Cos tie, 590
F.2d 1011 (D.C. Cir. 1978).
BAT Effluent Limitations
The factors considered in assessing BAT include the age of
equipment and facilities involved, the process employed, process
changes, and non-water quality environmental impacts, including
energy requirements [Section 304{b)(2)(B)]. At a minimum, the
BAT technology level represents the best economically achievable
performance of plants of various ages, sizes, processes, or other
shared characteristics. As with BPT, uniformly inadequate
performance may require transfer of BAT from a different
subcategory or category. BAT may include process changes or
internal controls, even when these technologies are not common
industry practice. The statutory assessment of BAT "considers"
costs, but does not require a balancing of costs against effluent
reduction benefits (see Weyerhaeuser v. Costle, supra). In
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developing the proposed BAT regulations, however, EPA has given
substantial weight to the rasonableness of costs. The Agency has
considered the volume and nature of discharges, the volume and
nature of discharges expected after application of BAT, the
general environmental effects of the pollutants, and the costs
and economic impacts of the required pollution control levels.
Despite this expanded consideration of costs, the primary
determinant of BAT is effluent reduction capability. As a result
of the Clean Water Act of 1977, 33 USC 1251, et seq., the
achievement of BAT has become the principal national means of
controlling water pollution due to toxic pollutants.
BCT Effluent Limitations
The 1977 Amendments added Section 301(b)(2)(E) to the Act
establishing best conventional pollutant control technology (BCT)
for discharges of conventional pollutants from existing
industrial point sources. Conventional pollutants are those
specified in Section 304(a)(4) [biological oxygen demanding
pollutants (BODS), total suspended solids (TSS), fecal coliform,
and pH], and any additional pollutants defined by the
Administrator as "conventional" (to date, the Agency has added
one such pollutant, oil and grease, 44 FR 44501, July 30, 1979).
BCT is not an additional limitation but replaces BAT for the
control of conventional pollutants. In addition to other factors
specified in Section 304(b)(4)(B), the Act requires that BCT
limitations be assessed in light of a two-part "cost-
reasonableness" test. American Paper Institute y_^ EPA, 660 F.2d
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954 (4th Cir. 1981). The first test compares the cost for
private industry to reduce its conventional pollutants with the
costs to publicly owned treatment works for similar levels of
reduction their discharge of these pollutants. The second test
examines the cost-effectiveness of additional industrial
treatment beyond BPT. EPA must find that limitations are
"reasonable" under both tests before establishing them as BCT.
In no case may BCT be less stringent than BPT.
EPA published its methodology for carrying out the BCT analysis
on August 29, 1979 (44 FR 50372). However, the cost test was
remanded by the United States Court of Appeals for the Fourth
Circuit. American Paper Institute y_._ EPA, 660 F.2d 954 (4th Cir.
1981). The Court of Appeals ordered EPA to correct: data errors
underlying EPA's calculation of the first test and to apply the
second cost test. (EPA had argued that a second cost test was
not required.) The Agency proposed a revised BCT methodology
October 29, 1982 (47 FR 49176) and a notice of availability of
additional data on September 20, 1984 (49 FR 37046). EPA expects
to promulgate the final methodology shortly.
New Source Performance Standards
The basis for NSPS under Section 306 of the Act is best available
demonstrated technology (BADT). New operations have the
opportunity to design and utilize the best and most efficient
processes and wastewater treatment technologies. Congress
therefore directed EPA to consider the best demonstrated process
changes, in-plant controls, and end-of-pipe treatment
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technologies that reduce pollution to the maximum extent
feasible.
Pretreatment Standards for Existing Sources
Section 307(b) of the Act requires EPA to promulgate pretreatment
standards for existing sources (PSES).
There are no ore mines, including gold placer operations, that
currently discharge to a POTW. By the nature of their locations,
it is unlikely that any indirect dischargers exist. Therefore,
no PSES are proposed at this time.
Pretreatment Standards for New Sources
Section 307(c) of the Act requires EPA to promulgate pretreatment
standards for new sources (PSNS) at the same time that it
promulgates NSPS. New indirect dischargers, like new direct
dischargers, have the opportunity to incorporate the BADT,
including process changes, in-plant controls, and end-of-pipe
treatment technologies, and to use plant site selection to ensure
adequate treatment system installation. Due to the location of
placer gold deposits, future operations are expected to be
located in rural areas far from any POTW. Therefore, no PSNS are
proposed at this time.
PRIOR EPA REGULATIONS
On 6 November 1975, EPA published interim final regulations
establishing BPT requirements for existing sources in the ore
mining and dressing industry (see 40 FR 41722). These
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regulations became effective upon publication. However,
concurrent with their publication, EPA solicited public comments
with a view to possible revisions. On the same date, EPA also
published proposed BAT and NSPS (see 40 PR 51738) for the ore
mining and dressing point source category, which included gold
placer mines.
On 24 May 1976, as a result of the public comments received, EPA
suspended certain portions of the interim final BPT regulations,
including the portion which applied to gold placer mines, and
solicited additional comments (see 41 FR 21191). EPA promulgated
revised, final BPT regulations for the ore mining and dressing
industry on 11 July 1978 (see 43 FR 29711, 40 CFR Part 440),
which reserved the section on gold placer mines. On 8 February
1979, EPA published a clarification of the BPT regulations as
they apply to storm runoff (see 44 FR 7953). On 1 March 1979,
the Agency amended the final regulations by deleting the
requirements for cyanide applicable to froth flotation mills in
the base and precious metals subcategory (see 44 FR 11546).
On 10 December 1979, the United States Court of Appeals for the
Tenth Circuit upheld the BPT regulations, rejecting challenges
brought by five industrial petitioners, Kennecott Copper Corp.,
y_,_ EPA, 612 F.2d 1232 (10th Cir. 1979). The Agency withdrew the
proposed BAT, NSPS, and pretreatment standards on 19 March 1981
(see 46 FR 17567).
On 14 June 1982, EPA again proposed BAT, BCT, and NSPS, again
reserving limitations for gold placer mines. On December 3,
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1982, final BAT and NSPS limitations for the ore mining point
source category were promulgated without limitations for gold
placer mines.
HISTORY OF REGULATION OF GOLD PLACER MINING
Effluent limitations guidelines and standards are not directly
enforceable against dischargers. Instead, they are incorporated
into a National Pollutant Discharge Elimination System (NPDES)
permit, which is required by Section 402(a)(l) of the Clean Water
Act for the discharge of pollutants from a point source into the
waters of the United States. If EPA^ has not established
industry-wide effluent limitations guidelines and standards to
cover a particular type of discharge, Section 402(a)(l) of the
Act expressly authorizes the issuance of permits upon "such
conditions as the Administrator determines are necessary to carry
out the provisions of this Act." In other words, this section
authorizes a determination of the appropriate effluent
limitations (e.g., BPT, BCT, BAT), on a case-by-case basis, based
on the Agency's "best professional judgment" (BPJ).
The establishment of technology-based effluent limitations in
NPDES permits is a two-step process. First, EPA must identify
the appropriate technology basis. The second step in the
permitting process is the setting of precise effluent limitations
which can be met by application of that technology. The Clean
Water Act does not require dischargers to install the technology
which is the basis of the limitations; dischargers may meet the
effluent limitations in any way they choose. In addition to
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technology-based standards, Sections 402 and 301(b)(l)(C) of the
Clean Water Act require a permit to include any more stringent
limitations including those necessary to meet water quality
standards established pursuant to any state law or regulation or
any other Federal law or regulation. Under Section 401 of the
Act, no NPDES permit may be issued unless the state has granted
or waived certification that the discharge will comply with the
applicable provisions of the Act; if the state includes
conditions as part of its certification, EPA must include those
conditions in the permit.
1. The 1976-1977 BPT Permits
In 1976 and 1977, EPA issued 170 permits to Alaska placer miners.
Because there were no effluent limitations guidelines promulgated
for the placer mining industry at that time, these permits were
based on BPJ. In addition, these permits included limitations
designed to satisfy Alaska's water quality standards.
Each of the permits had identical effluent limitations,
monitoring requirements, and reporting requirements,, The permits
required treatment of process wastes so that the maximum daily
concentration of settleable solids was 0.2 milliliters per liter
(ml/1). In addition, the permits required monthly monitoring for
this pollutant or instead of monitoring to establish compliance
with the settleable solids limitation, each permittee was given
the option of installing a settling pond with the capacity to
hold 24 hours' water use. In addition, the permittee could not
cause an increase in turbidity of 25 JTU (Jackson Turbidity
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Units) over natural turbidity in the receiving stream at a point
measured 500 feet downstream from the final discharge point. EPA
added the turbidity limitation at the request of the State of
Alaska, which included this requirement in its certification of
these permits under Section 401 of the Clean Water Act, to ensure
compliance with its state water quality standards. The
technology basis for the settleable solids limitation was
settling ponds.
In June 1976, Gilbert Zemansky requested an adjudication of the
1976 NPDES permits as an interested party. Subsequently, the
Trustees for Alaska (Trustees) and the Alaska Miners Association
(Miners), as well as others, were admitted as additional parties
to the proceeding. The Trustees and Zemansky argued that the
permit terms were not stringent enough and that EPA should have
selected recycle as the model BPT technology and required zero
discharge of any pollutants, while the Miners argued that the
terms were too stringent and not achievable. After the initial
adjudicatory hearing, the Regional Administrator for Region X
issued his Initial Decision on October 25, 1978, upholding the
terms of the permits.
The Trustees, Zemansky, and the Miners each petitioned the
Administrator of EPA to review the initial decision. On March
10, 1980, the EPA Administrator issued his decision on review.
The Administrator held that the Regional Administrator's findings
regarding settling pond technology "conclusively establish that
any less stringent control technology does not satisfy the
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requirements of BPT." Decision of the Administrator (Ad. Dec.).
Ad. Dec. at 15. The Administrator also found that "the Regional
Administrator was in doubt about the facts respecting the extra
costs of recycling ...." Therefore, the Administrator remanded
the proceedings to the Regional Administrator "for the limited
purpose of reopening the record to receive additional, evidence on
the extra cost of recycling in relationship to the effluent
reduction benefits to be achieved from recycling." Ad. Dec. at
22. The Administrator directed the Regional Administrator to
determine whether recycling constitutes BPT based on the
additional evidence received.
After the Administrator rendered his decision, the Trustees
requested the Administrator to: (1) determine the effluent
limitations necessary to meet state water quality standards; (2)
determine appropriate effluent monitoring requirements in the
event the Regional Administrator did not determine that zero
discharge was required; and (3) direct the Regional Administrator
on remand to determine effluent limitations for total suspended
solids or turbidity, for arsenic, and for mercury based on BPT in
the event he did not determine that zero discharge is required.
On July 10, 1980, the Administrator issued a Partial Modification
of his decision, directing the Presiding Officer "to allow
additional evidence to be received if he determines on the basis
of the record that such additional evidence is needed to make the
requested determinations." Partial Modification of Remand at 3.
The hearing on remand was held in March and June 1981, and the
Presiding Officer issued his Initial Decision on Remand (Rem.
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Dec.) on March 17, 1982. After reviewing the costs and effluent
reduction benefits associated with both settling ponds and
recycle, the Presiding Officer held that "the preponderance of
the evidence in this case indicates that zero discharge is not
'practicable* for gold placer miners in Alaska." Rem. Dec. at
17. He also ordered EPA to modify the permits to include
monitoring requirements for settleable solids and turbidity, and
to require monitoring for arsenic and mercury, for at least one
season, "to determine whether or not [they] constitute a problem
with placer mining." Rem. Dec. at 19-20.
On September 20, 1983, the Administrator denied review of the
Initial Decision on Remand. Both the Trustees for Alaska and
Zemansky, as well as the Alaska Miners Association, petitioned
the Ninth Circuit Court of Appeals for review. (Case No. 83-7764
and Case No. 83-7961). The Ninth Circuit consolidated the cases
and issued its decision in Trustees for Alaska v. EPA and Alaska
Miners Association v. EPA on December 10, 1984 (749 F.2d 549).
In this court proceeding, the Miners raised various legal issues,
including certain constitutional challenges, each of which was
dismissed by the Court. Specifically, the Court held that: (1)
the Clean Water Act's permit requirements applied to placer
mining, i.e., when discharge water is released from a sluice box
it is a point source; (2) EPA's failure to establish effluent
limitations guidelines and standards for the placer mining
industry could only be challenged in district court; and (3) the
Miners' challenge to the assignment of the burden of proof in the
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administrative hearings was not timely; it should have been
raised when the permit regulations establishing that standard
were promulogated.
The Court also dismissed the Miners' constitutional claims as too
speculative or premature. The Miners had claimed, e.g., that the
permit conditions constituted a taking of their vested property
rights in violation of the Fifth Amendment; the permits' self-
monitoring, reporting, and recordkeeping provisions infringed
their constitutional privilege against self-incrimination; and
the permits' inspection provisions infringed their rights under
the Fourth Amendment to be free from unreasonable searches.
The Court dismissed most other challenges to the permits as moot
since the permits expired before this case reached the Ninth
Circuit, and EPA had issued two sets of subsequent permits (in
1983 and 1984) based on newer, more complete records by the time
the Court heard this case. The Court specifically held that
EPA's choice of settling ponds as "best practicable control
technology" (BPT) was moot because a different standard, "best
available technology" (BAT), now applies.
However, the Court held that the form of the limitations included
in the permits to ensure achievement of state water quality
standards was not moot since both the permits at issue and the
subsequent permits incorporated state water quality standards
directly into the permits. After reviewing the definition of
"effluent limitation," the legislative history of the 1972
amendments to the Clean Water Act, and relevant court cases, the
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Court held that EPA should not have incorporated the state water
quality standard for turbidity, which was a receiving water
standard, directly into the permits. Instead, the Court held
that the permits must include end-of-pipe effluent limitations
necessary to achieve the water quality standards. The Court also
held that EPA should have given the Trustees the "opportunity to
present in a public hearing their case for proposed effluent
limitations or monitoring requirements for arsenic and mercury."
2. The 1983 Permits
During the proceedings on the 1976-1977 permits, EPA issued
additional permits to Alaskan placer miners. In 1983, EPA issued
269 new permits. The 1983 permits were issued for the 1983
mining season and differed from the 1976 permits in several
respects. For example, the 1983 permits contained a daily
maximum discharge limit of 1.0 ml/1 and a monthly average
discharge limit of 0.2 ml/1 on settleable solids. The 1983
permits also included a limit on arsenic based on the Alaska
state water quality standards.
The Trustees for Alaska and Gilbert Zemansky requested an
evidentiary hearing on the 1983 permits which the EPA Region X
Regional Administrator granted. On Febraury 16, 1984, the
proceedings were dismissed for several reasons, including
expiration of the 1983 permits and the Agency's intent to issue
new permits that would take effect in the next mining season
(i.e., the summer of 1984). No one appealed the decision within
the Agency or petitioned for judicial review of the decision.
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3. The 1984 and 1985 Permits
In 1984, EPA issued BAT permits to 445 placer miners (the first
set was issued on June 8, 1984; additional permits were issued on
June 14, 1984). The technology basis for the BAT permits, like
the BPT permits, is settling ponds. Based on additional data
developed since the BPT permits were issued, the instantaneous
maximum settleable solids discharge limit is 1.5 ml/1 and the
monthly average limit is 0.7 ml/1. Monitoring is required twice
per day, each day of sluicing. The permits incorporate Alaska's
state water quality standards for turbidity and arsenic and
require visual monitoring for turbidity.
On January 31, 1985, in response to the Ninth Circuit opinion
which held that permits must include end-of-pipe effluent
limitations necessary to achieve state water quality standards
(see above), EPA proposed to modify the 1984 permits to include
effuent limitations for turbidity (5 NTU's above background) and
arsenic (0.05 mg/1). On February 12, 1985, EPA proposed permits
for 93 additional mines. These permits proposed the same
limitations as the 1984 permits, except they include the effluent
limitations for turbidity and arsenic just mentioned rather, than
simply citing the state water quality standards. On May 10,
1985, EPA issued both the modified permits to miners holding
permits in 1984 and the new permits to the 1985 applications.
Various parties have challenged these permits; they are currently
being adjudicated.
INDUSTRY OVERVIEW
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Placer mining consists of excavating waterborne or glacial
deposits, e.g., gold-bearing gravels or sands, which can then be
separated by physical or gravity separation means (e.g.,
sluices).
The industry includes operations employing various dredging
techniques (including clam shell, continuous bucket, dragline or
suction dredges) and hydraulic (i.e., water cannons).
Alaska
The Alaskan gold placer mining industry is thought to have over
700 operations (Reference 1) although only about 540 operations
applied for NPDES permits in 1985. Reference 2 indicates that
there were 304 active placer gold operations in Alaska in 1982
with an estimated annual production in excess of 160,000 troy
ounces. Most of these operations are intermittent or seasonal
and many would be classifed as recreational or week-end
operations.
Idaho
Based upon a review of application for dredging and placer mining
permits in Idaho and other information in the Idaho Department of
Land files (Reference 3), there are approximately 29 active gold
placer mines and 42 inactive mines in the state. Twenty-seven of
the 29 active operations are located in ten counties with the
majority of these (19) located in two counties. The volume of
ore sluiced per day ranges from approximately 36 cubic yards to
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4,800 cubic yards, with the sizes and types of operations being
basically similar to those in Alaska and Montana. Most of the
mines use open cut methods, but there are also at least three
large-scale dredging operations.
Montana
There are 50 gold placer mines (employing mechanical, open-cut
methods) in Montana which have discharge permits or are otherwise
known to exist. It is likely that there may be another 60 mines
that do not have discharge permits (some may not discharge
wastewater). The mines are located in the western portion of of
the state. There are no known hydraulic mining operations or
mechanical dredges operating in Montana. However, the Montana
Department of Health and Environmental Sciences has issued water
discharge permits to approximately 97 suction dredges, which
generally are quite small (2- to 4-inch diameter). The mining
methods, classification methods, wastewater treatment
technologies, and size of the operations all appear similar to
those encountered in Alaska (Reference 4).
Colorado
A review of the Colorado Water Pollution Control Division's files
indicated that only four gold placer mines in the state had
permits to discharge wastewater. Other sources indicate that
there may be as many as 19 more mines in the state (Reference 5).
This apparent discrepancy may be explained by several
possibilities including: (a) no discharge of wastewater; (b)
inactive status; (c) improper classification as a placer mine;
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and (d) discharge without a permit. The mines for which permits
have been issued are relatively small (less than 150 cubic
yards/day), seasonal, open-cut mines employing settling ponds for
treatment of wastewater.
California
According to the U.S. Bureau of Mines (Reference 6), one large
dredging operation was expected to recover 20,000 to 25,000 troy
ounces of gold annually. There are likely to be other
operations, but no data on these operations are available. It
has been estimated that there may be as many as 25 operating
mines in California, but all are thought to be zero discharge
operations.. (Reference 7).
Nevada
According to Reference 6, 157 troy ounces of gold were obtained
from placer deposits in Nevada. However, little is known about
any active placer operations. It has been estimated that there
are six commercial placer mines in Nevada (Reference 7).
Oregon
Several small placer mines are small suction dredges were
reported as operating along gold-bearing drainages in
southwestern Oregon (Reference 6). Production is unknown. It is
thought that there may be 25 to 50 operations in Oregon
(Reference 7).
Washington
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It has been estimated that there are 30 operating placer mines in
Washington, but little is known about them. No state discharge
standards are in effect.
For purposes of this document and the proposed limitations and
standards, EPA is creating a separate subcategory in the ore
mining and dressing point source category known as "gold placer
mining" to include placer mining operations which process more
than 20 cubic yards per day by gravity separation methods,
including hydraulic mining, suction dredge mining, and all
mechanical mining practices.
The 20-cubic-yard-per-day cutoff would exclude the smaller
recreational or assessment operations. This proposed regulation
also does not cover mining in marine waters or in the coastal
zone (beach) because: (1) the Agency does not, at present, have
a data base adequate to address this group; and (2) the
limitations that might be developed may require different
conditions because of uncertainty about the technology employed,
the reasonableness of various treatment alternatives, and the
potential need to protect certain marine water resources.
GENERAL APPROACH AND METHODOLOGY
From 1973 through 1976, the EPA Effluent Guidelines Division
attempted to obtain data on Alaskan gold placer operations as
part of its general study of the ore mining and dressing point
source category. Because the industry itself was so large and
diverse, the Agency determined after promulgating interim final
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BPT limitations that the data base on placer gold operations, in
general, and placer gold operations in Alaska, Colorado, Montana,
California, Idaho, Washington, Oregon, and Nevada, in particular,
were inadequate to form the basis of national effluent
limitations guidelines and standards. From 1977 through the
present, the Agency itself and its contractors have undertaken
several sampling surveys and data collection efforts aimed at
resolving various issues. The following paragraphs briefly
describe the major study tasks and their results as presented in
this report.
Industry Data Base Development and Subcategorization Review
First, EPA studied the gold placer mining industry to determine
whether there were differences in type of deposit, processes
employed, equipment used, age and size of operations, water
usage, wastewater constituents, or other factors indicating the
need to develop separate effluent limitations and standards for
different segments of the industry. This study included
identification of raw wastewater and treated effluent
characteristics, including: the sources and volume of water
used, the processes employed, and the sources of pollutants and
wastewater and the constituents of wastewater, including toxic
pollutants. EPA then identified the constituents of wastewaters
that should be considered for effluent limitations guidelines and
standards of performance. EPA was aided in this study by having
previously examined and sampled (for a 10-year period) the ore
mining industry in general and various operations in the gold
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mining subcategory in particular. The data from these studies
were useful in selecting the pollutants (conventional,
nonconventional, and toxic) that should receive emphasis in the
sampling programs.
Next, EPA identified several distinct control and treatment
technologies that are in use or capable of being used in the
placer mining segment. The Agency compiled and analyzed
historical and newly generated data on effluent quality resulting
from the application of these technologies. The long-term
performance, operational limitations, and reliability of each
treatment and control technology were also identified. In
addition, EPA considered the non-water quality environmental
impacts of these technologies, including impacts on air quality,
solid waste generation, water availability, and energy
requirements.
Data Gathering Efforts.
Data collected for the placer mining industry included extensive
studies:
1. KRE Treatability Study - 1984
2. KRE Reconnaissance Study - 1984
3. EPA Region X - 1984 Reconnaissance Study
4. FTA Reconnaissance Study - 1984 (Lower 48)
5. Shannon and Wilson - 1984 Wastewater Treatment
Technology Project
6. FTA and KRE - 1983 Treatability Studies
7. Dames and Moore - 1976 Reconnaissance Study
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8. Calspan Corp. - 1979 Reconnaissance Study
9. EPA/NEIC - 1977 Reconnaissance Study
10. ADEC - 1977, 1978, 1979 Reports
11. R&M Consultants - 1982 Treatability Study, Site Visits,
and Fond Design Manual (for ADEC)
12. EPA Region X - 1982 Reconnaissance Study
13. EPA Region X - 1983 Reconnaissance Study
14. Canadian Dept. Env. - 1981 and 1983 Yukon Studies
These studies are described in detail in later sections of this
document. In all, over 100 mines representing operations in
several states have been sampled.
Subcategorization Review.
Section IV outlines the factors considered in potential
Subcategorization. Two subcategories or segments were
recommended for exclusion: (1) operations processing less than
20 cubic yards per day, and (2) marine or coastal zone
operations.
Sampling Program
The collection of detailed analytical data on conventional,
nonconventional, and toxic pollutant concentrations in raw and
treated process wastewater streams was completed in a
comprehensive sampling program. The sampling and analytical
methodology is described in Section V. The BPT and BAT
development efforts showed that organic priority pollutants would
not be expected to be significant in this industry group.
Therefore, the sampling programs undertaken by the various groups
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were modified to emphasize certain pollutants.
Wastewater Characteristics
The results of the historical and recent effluent data collection
efforts are summarized in Section VI. Particular emphasis has
been placed upon 1983 and 1984 data.
Treatment System Cost Estimates
Section IX presents the general approach to cost estimating,
discusses the assumptions made, and gives the detailed cost
estimates for alternative levels of treatment and control. For
each subcategory, the total estimated installed cost of typical
treatment systems is developed on the basis of model plant design
specifications. Estimated incremental costs are given for each
of the advanced level treatment alternatives. The Agency then
estimated the cost impact of installation of the various
treatment alternatives.
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REFERENCES
1. USEPA - Region X, "Draft General NPDES Permit for Placer
Mining in the State of Alaska," February 14, 1983.
2. Alaska Office of Mineral Development, "Alaska's Mineral
Industry - 1982," Special Report 31, 1993.
3. Harty, D. M., Frontier Technical Asso., Inc., Letter to
B. M. Jarrett, USEPA - ITD, November 30, 1984.
4. Harty, D. M., Frontier Technical Asso., Inc., Letter to
B. M. Jarrett, USEPA - ITD, November 16, 1984.
5. Harty, D. M., Frontier Technical Asso., Inc., Letter to
B. M. Jarrett, USEPA - ITD, November 5, 1984.
6. Minerals Yearbook ^ 1982, Volume 1, "Metals and
Minerals," U.S. Bureau of Mines, 1983.
7. Harty, D. M. and Terlecky, P. M., Frontier Technical Asso.,
Inc., Letter to B. M. Jarrett, USEPA - ITD, March 5, 1984.
8. USEPA - Region X, "Draft of General NPDES Permit for Placer
Mining in the State of Alaska," February 1984.
9. USEPA - Response report as a result of public hearings held
in Fairbanks, Alaska, on April 3 and 5, 1984.
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SECTION III
INDUSTRY PROFILE
HISTORICAL PERSPECTIVE
Discovery and Exploitation
Prior to the Alaska purchase in 1867, the existence of placer
gold in Alaska was known to the Russians, the English of the
Hudson Bay Company, and members of the Western Union Telegraph
exploration party, but little exploitation of these deposits took
place (1). The placer gold industry in Alaska was started
primarily by California gold rush prospectors moving up the
coast. Significant events which stimulated this industry were
gold discoveries in the Juneau vicinity (1880), Rampart (1882),
Forty-mile district (1886), and Birch Creek (Circle) district
(1893). The Klondike gold rush of 1897-1898 in Canada also
stimulated Alaskan prospecting. Additional deposits were
discovered in Nome (1898), Fairbanks (1902), and the Tolovana
(Livengood) district (1914). High-grade deposits were mined out
rapidly, but the introduction of large-scale permafrost thawing,
hydraulic stripping, and mechanized excavation methods increased
the productivity of placer mining and allowed working of lower-
grade deposits (1). Mechanical dredges were introduced in Nome
in 1905 and large electric-powered dredges were employed in Nome
and Fairbanks in the 1920's,
In 1940, Alaska wan the leading gold-producing state with
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production of 750,000 troy ounces,* mostly from placer mines.
*One troy ounce is equal to 31.1 grams (1.097 ounces
avoirdupois).
Placer mining activity was substantially reduced during World War
II, and operations after the war remained at a low level because
of rising operating costs and a government-fixed gold price of
$35 per troy ounce. Dredging was reduced to only a few
operations in the 1960's. Relaxation of federal restrictions on
prices and private ownership of gold in the 1970's and an
increase in the market price stimulated gold mining activity in
the later 1970's; several hundred placer mines came into
operation. In 1982, gold production was more than 160,000 troy
ounces from placer mining alone (total Alaskan gold production
for 1982 from lode and placer mines was in excess of 175,000 troy
ounces).
Almost all of the gold produced in the United States outside of
Alaska is produced in the following 17 states: Alabama, Arizona,
California, Colorado, Georgia, Idaho, Montana, Nevada, New
Mexico, North Carolina, Oregon, South Carolina, South Dakota,
Utah, Virginia, Washington, and Wyoming. Gold mining in the
United States began in North Carolina, with Georgia joining in
production in 1829, and Alabama in 1830. Production began in
other states as prospectors moved west. The most important gold
discovery, because of its influence on western development, was
at Sutter's Mill in California in 1848. Later discoveries were
made in most other Western states and territories.
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Early mining was largely by placer methods with miners working
stream deposits by various hydraulic techniques. The gold was
recovered by gravity separation or by amalgamation with mercury.
During the period 1792 through 1964, 88 percent of the production
came from gold ores (51 percent - lode; 37 percent - placers) and
12 percent as a byproduct from other metal mines. The total U.S.
gold production as of 1980 was 319 million ounces with lode gold
mining supplying about 50 percent, placer mining 35 percent, and
base metal mining (byproduct) accounting for 15 percent (2).
Lode mining is defined as "hard rock" mining using either open
pit or underground methods of mining minerals that are in place
as originally deposited in the earth's crust or that have been
reconsolidated into a composite mass with waste rock. The sought
after mineral is not in a "free" or loose state.
Gold Prices
Gold prices during the last 20 years have been subject to wide
variation as illustrated below:
Year Tr.Oz.
1934 - 1968 $ 35
1974 (Dec.) 200
1975 (Dec.) 162
1977 (Dec.) 161
1978 (Dec.) 208
1979 (Nov.) 392
1980 (Jan.) >800
1982 (Mar.) 315
1983 (Dec.) 390
1984 (Dec.)* 315
The industry should be viewed against the backdrop of fluctua-
ting prices since rising prices stimulate prospecting, dictate
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the number of active operations, cause increases in production/
and allow the mining of lower grade ores, while decreasing prices
have the opposite effects.
*Wall St. Journal (12/18/84)
DESCRIPTION OF THE INDUSTRY
Nature of_ Deposits
Placer mining is the process involved in the extraction of gold
or other metals and minerals from alluvial deposits which may be
from recent ("young" placers) or ancient deposits ("old,"
"ancient," or "fossil" placers). Currrent placer mining activity
generally takes place in young placers originating as waterborne
or glacially-deposited sediments. For many years, gold has been
the most important product obtained, although considerable
platinum, silver, tin (as cassiterite, Sn02), phosphate,
monazite, rutile, ilmenite, zircon, diamond and other heavy,
weather-resistant metals or minerals have been produced from
these deposits at various locations in the world. Since gold has
a high specific gravity (19.3), it settles out of water rapidly
and is found associated with other heavy minerals in the
deposits.
Most placer deposits consist of unconsolidated or semiconsoli-
dated sand and gravel that actually contain very small amounts of
native gold and other heavy minerals. Most are stream deposits
and occur along present stream valleys or on benches or terraces
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of pre-existing streams (4). Placer gold deposits are also
occasionally found as beach or offshore deposits as at Nome/
Alaska.
Residual placers are defined as deposits found spread over a
local gold bearing lode deposit as a residual of the decay or
erosion of that deposit and are found at a number of localities
such as Flat/ Happy/ and Chicken Creeks in the Iditarod District
of Alaska/ but have not been an important source of gold. Creek
bench deposits are found in virtually all the districts. Modern
creek placers occupy the present creek channels and usually
contain gravels from a few feet to 10 feet or more thick. The
ancient placers are those in benches or terraces along present
streams. The deeply buried channels or "deep gravels" are
deposits of ancient streams which are now buried by alluvium.
The best examples of these deposits are in the interior of
Alaska, particularly in the Fairbanks, Hot Springs, Tolovana, and
the Yukon-Tanana region. The gravels are ordinarily 10 to 40
feet thick but are buried under "muck" or black humus, fine gray
sand/ silt/ and clay which may be 10 to 30 feet or more thick
(5).
Bench placers have the characteristics of modern creek placers
but are higher than the present bed of the stream. Present
streams have cut into the deposits forming surface terraces that
resemble benches. High-bench deposits result from the action of
streams of a former drainage system with no direct relation to
existing drainage channels. These high gravels are sometimes
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called "bar" deposits. Some of the best examples are in the
Rampart, Hot Springs, and Ruby Districts. Some of the high bench
deposits near Nome between Dexter and Anvil Creeks have been very
productive (5).
Beach placers are resorted deposits that have been formed by wave
action which erodes adjacent alluvial deposits and concentrates
their gold along the beach. Examples of these deposits are at
Lituya Bay, Yakataga and Kodiak Island. The most important beach
placers are at and near Nome. At Nome, there are both submerged
and elevated beach placers formed at times particularly over the
last million years when sea level fluctuated. In most cases, the
beach lines, usually gravels, covered with muck and overburden,
have been very productive. Their thickness ranges from 30 to 100
feet (5).
Other types of placers include river bar, gravel plain, those
associated with bedding planes and crevices of the bedrock, and
some placers in which the bedrock has formed or is overlain by a
sticky clay or "gumbo" in which the gold may be distributed (5).
The presence of beds of clay or "hardpan" in placer deposits may
influence the distribution of the gold. The clay beds form
impervious layers on which concentration of gold takes place and
prevent the gold from working below them (6).
Location
According to a study conducted by Louis Berger arid Associates
(7), placer mining is more than twice as important: in the area
north of the Alaska Range (with Fairbanks as the center of placer
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Table lli-l.
Mineral Activity in Alaska by Mining Camp
as of 1982 (Source: Ref. 7).
Map
No.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
$%
Camp
(b)
Gold
Production Discovery Map
(tr. oz.) tote No.
Nome
Solomon
Bluff
Council
Koyuk
Fairhaven (Candle)
Fairhaven (Inmachuk)
Kbugarok
Port Clarence
Naatak
Kobuk (Squirrel River)
4,348,000
251,000
90,200
588,000
52,000
179,000
277,000
150,400
28,000
39,000
7,000
Kobuk (Shungnak) 15,000
Koyukuk (Hughes) 211,000
Koyukuk (Nolan) 290,000
Chandalar 35,708
Marshall (Anvik) 120,000
Goodnews Bay 29,700
Kuskokwim (Aniak) 230,600
Kuskokwim (Georgetown) 14,500
ftiskokwim (McKinley) 173,500
Iditarod 1,364,404
Innoko 400,000
Iblstoi 87,200
Iliamna (Lake Clark) 1,500
Skwentna (included in
Yentna production)
Yentna (Cache Creek) 115,200
Kantishna 65,000
Ruby ' 420,000
Gold Hill 1,200
Hot Springs 450,000
Rampart 105,000
Tblovana 387,000
Fairbanks 7,940,000
Chena (included in
Fairbanks production)
$%
1898
1899
1899
1897
1899
1901
1900
1900
1898
1898
1909
1898
1910
1893
1905
1913
1900
1901
1909
1910
1908
1906
1902
1905
1903
1907
1907
1898
1882
1914
1902
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
Camp
(b)
Gold
Production
(tr. oz.)
Discovery
tote
Bonnifield 50,000 1903
Richardson 103,000 1905
Circle 800,000 1983
Wbodchopper-Coal Creek
(included in Circle production)
Seventymile (included in Fortymile
production)
Eagle 45,000 1895
Fortymile 417,000 1886
Valdez Creek 44,000 1904
Delta 2,500
Chistochina-Chisna 177,000 1898
Nabesna 93,500 1899
Chisana 50,000 1910
Nizina 143,500 1901
Nelchina 2,900 1912
Girdwood 125,000 1895
Hope (included in Girdwood)
production)
Kodiak 4,800 1895
Yakataga 15,709 1898
Yakutat 2,500 1867
Lituya Bay 1,200 1867
Porcupine 61,000 1898
Juneau(Gold Belt) 7,107,000 1880
Retchikan-Hyder 62,000 1898
Sundum 15,000 1869
Glacier Bay 11,000
Chichagof 770,000 1871
Willow Creek 652,052 1897
Prince William Sd. 137,900 1894
Unga Island 107,900 1891
(a)-Ccmpiled from U.S. Geological Survey publications, U.S. Bureau of Mines records,
Alaska Division of Geological and Geophysical Survey records and publications,
Mineral Industry Research Laboratory research projects, and other sources.
(b)-Camp names are those that appear in official recording-district records. Many
are also known by other names, some of which are shown in parentheses.
-------
mining activity) compared to the area south of the range. Other
centers where placer mining activity is important in Alaska are
Nome, Glenallen, Talkeetna, Palmer, Ruby, Circle, Hot Springs,
and Juneau (7). Figure III-l and Table III-l taken from
Reference 7 illustrate the principal placer mining areas of the
state and some salient statistics concerning them.
Production
Accurate production figures for the Alaskan gold placer mining
industry have been difficult to obtain in the past. Historically,
Bureau of Mines figures tend to underestimate what the actual
production has been based upon field surveys and surveys by the
State of Alaska.
Most placer deposits contain a few cents to several dollars worth
of gold per cubic yard (1 cubic yard weighs about 1.5 tons); a
rich placer deposit would contain only a few grams of gold per
ton of gravel. The largest placer deposits have yielded several
million ounces of gold, but most have been much smaller (4). The
Bureau of Mines has estimated that placer deposits contributed as
much as 3 percent of the U.S. total annual production in 1982,
but reliable estimates of Alaskan placer gold production
apparently are difficult to obtain. Taking the State of Alaska's
1982 estimates of placer production (I) and comparing them to the
Bureau of Mines 1982 total gold production (latest year published
- see Reference 8) indicates that Alaska placer deposits may
contribute approximately 10 percent (or more) of total U.S. gold
production. The majority of this gold may not end up as bullion
III-7
-------
-11-
1100
1000
900-
800-
700-
" 600-
X
I 500-
§
I 400-
o
a 300-
200-
100-
Total production
30 million OUHCM
•
r 70
- 65
60
55
50
\- 45
40
h 35
30
• 25
20
15
10
5
c
n
Q.
•s
IQ
1
o
r*
o'
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1900
Figure III-2.
Year
Gold Production and Value of Production
in Alaska for 1880-1982 (Source: Ref. 1)
-------
production, however? most probably finds its way into the jewelry
market.
Figure 111-2 from Reference 1 is a plot of historical gold pro-
duction and value in Alaska for the period 1880-1982. Based upon
recent estimates, placer gold production in Alaska exceeded
160,000 troy ounces in 1982 and probably accounted for nearly 95
percent of total gold production from both lode ores and placers
(1).
Number of_ Operations
The total number of active placer gold operations in Alaska is
difficult to determine. The EPA estimated in 1983 that there
were over 700 operations although only about 250 applied for
water discharge permits (3).
EPA Region X issued 446 permits in 1984. None of these are for
mines processing less than 20 cubic yards per day. Perhaps the
best estimate of the number of operations may be obtained by
review of the so-called "tri-agency" forms for placer mining.
This form is required by the Alaska Department of Natural
Resources, the Department of Environmental Conservation, and the
Department of Fish and Game for any working mine. It serves as
an annual application for a land use and water use permit and for
a mining license. The tri-agency form requires information
concerning the owner and operator of the mine, location, method
of operation, equipment, and employment, among other data (7).
There were 507 tri-agency applications submitted in 1982. A
III-8
-------
breakdown of these operations is given below (7):
Category* Employees Number of Operations
Recreational or 1-3 137
Assessment (R/A)
Small 3-4 238
Medium 4-7 120
Large >6 12
Total 507
*Size based upon annual expenditures for operating expenses:
R/A - <$10,000; Small - $10,000 to $125,000; Medium - $125,000
to $800,000; Large - >$800,000.
An independent survey by the Alaska Division of Geological and
Geophysical Surveys estimated that there were at least 304 active
placer gold operations in 1982 (1). This figure can be compared
to a total of 370 mines resulting from subtracting the number of
recreational mines (137) from the total number of tri-agency
applications. It should also be pointed out that the use of the
tri-agency form has two limitations: (1) it indicates the
miner's intentions before the mining season begins but does not
necessarily reveal actual mining activities, and (2) a number of
operators of recreational, assessment, and other small miners may
not always complete and file the forms (7).
Section II, "Introduction," outlines what information is
available on the number of operations in other states besides
Alaska. Additional data on individual operations for Alaska and
other states are presented in tables at the conclusion of this
section.
III-9
-------
SUMMARY OF MINING AND PROCESSING METHODS
General
The mining and processing methods in use today in Alaska and the
other gold placer mining states are similar in many respects to
those in use elsewhere in the ore mining and dressing industry.
Three important differences exist in this segment, namely: (a)
the nature of the deposits - a great deal of material must be
excavated or moved and then processed to remove an accessory or
trace constituent (gold), and because gravity separation methods
are used, this requires a great deal of water per unit or
production; (b) the climate and location of many operations
dictate harsh operating conditions and constant maintenance; (c)
permanently frozen overburden and deposits must be thawed in
order to be exploited.
The actual mining season varies with location and availability of
water but generally ranges between 85 to 137 days with the
average operation probably in the 100 to 115 operating day range.
This range is most typical for operations in the industry as a
whole, but there are a few operations in the contiguous states
which operate with long seasons (270 days) or even year-round.
Before 1930, opencut placer mines operated with steam-powered
shovels, scrapers, draglines, cableway excavators, and
reciprocating and pulseometer pumps. The development of the
lightweight diesel engine, which resulted in the advent of
diesel-powered bulldozers, draglines, and pumps brought about a
revolution in opencut placer mining methods in Alaska (9), as
111-10
-------
well as other states.
The introduction in the mid-1930's of efficient modern exca-
vating equipment and portable centrifugal pump units made it
possible to work many deposits that could not be mined earlier by
the more cumbersome machines. Improvements in gravel washing and
recovery systems were developed simultaneously.
Readily movable steel sluiceboxes with hoppers and grizzlies,
mounted on steel trestles with skids, replaced awkward and less
desirable wooden structures. The steel sluiceplate, often called
the slick plate, was one of the most influential improve-ments;
it was responsible for the development of simple and flexible
mining techniques. The use of portable diesel-driven centrifugal
pumps allowed the recirculation of wastewater to supplement
limited water supplies. Utilization of draglines and bulldozers
in combination with established hydraulic methods facilitates the
removal of both frozen and thawed overburden as well as the
handling of gravel and bedrock during sluicing. Improved dryland
dredges, using revolving trommels and stacker conveyors mounted
on crawler-type tracks, were developed into successful washing
and recovery devices at several properties (9).
The choice of excavation equipment, recovery system, and
arrangement of the mining method is based essentially upon the
size and physical characteristics of the deposits as well as on
the water supply, the ultimate choice depending on the funds
available for initial capital investment and the personal
preference of the operator (9).
Ill-ll
-------
Mining Methods
Dredging Systems. Dredging systems are classified as hydraulic
or mechanical depending upon the method of digging, and both are
capable of high production. A floating dredge consists of a
supporting hull with a mining control system, excavating and
lifting mechanism, beneficiation circuits, and waste-disposal
systems. These are all designed to work as a unit to dig,
classify, recover values, and dispose of waste (10).
a. Hydraulic Dredging Systems. Whether the lifting force is
suction,suction with hydrojet assistance, or entirely hydrojet,
hydraulic dredging systems have been used much less frequently in
placer mining than mechanical systems.
However, in digging operations where mineral recovery is not the
objective, the hydraulic or suction dredge has greater capacity
per dollar of invested capital than any mechanical system because
the hydraulic system both excavates and transports. The
hydraulic dredge is superior when the dredged material must be
moved some distance to the point of processing. Because it is
much more economical to treat the placer gravels aboard the
dredge, the hydraulic systems with their inherent dewatering
problems are at a disadvantage (10).
Hydraulic digging is best suited to relatively small-size loose
material. It has the advantage over mechanical systems in such
ground when the material must be transported from the dredge
whether by pipeline or barge. In easy digging, excavation by
111-12
-------
hydraulic systems has reached depths of about 225 feet, but
excavation for mineral recovery to date has been much less, only
about one-quarter of that depth. The interest in offshore mining
has stimulated the development of hydraulic dredging equipment.
Even with efficiently designed units and powerful pumps, the size
of the gold that can be captured by hydraulic dredging is
limited. The ability of a hydraulic system to pick up material
in large part depends upon intake and transport velocities that
must be increased relative to specific gravity and size of
particles. If the gold occurs as nuggets, especially large
nuggets, the velocity required for capturing the gold can cause
excessive abrasion in the entire system. In addition, higher
velocities require more horsepower. On the other hand, when the
flake size of the gold is very fine, higher velocities make gold
recovery very difficult during dewatering.
The digging power of hydraulic systems has been greatly in-
creased with underwater cutting heads. One disadvantage of a
cutterhead is that it must be designed with either right- or
left-hand cutting rotation, which results in less efficient
digging when the dredge is swung in one direction, especially in
tough formations. As digging becomes more difficult and the
cutterhead is swung across the face in the direction so that its
blades are cutting from the old face to the new, the cutterhead
tries to climb onto and ride the scarp. This produces con-
siderable impact stress through the power-delivery system and
reduces the capacity of the cutter. Because hydraulic dredges,
even with cutterheads, dig less effectively than mechanical
111-13
-------
dredges, gold particles which are trapped in bedrock crevices are
more difficult to recover (10).
The principal uses of hydraulic dredges have been for nonmining
jobs such as in digging, deepening, reshaping, and maintaining
harbors, rivers, reservoirs, and canals; in building dams and
levees; and in landfill and reclamation projects. Hydraulic
systems in mining have been used to produce sand and gravel, mine
marine shell deposits for cement and aggregate, reclaim mill
tailings for additional mineral recovery, and to mine deposits
containing diamonds, tin, titanium minerals, and monazite (10).
(b) Mechanical Dredging Systems. Digging systems on continuous
mechanical dredges can be a bucket-ladder, rotary-cutter, or
bucket-wheel excavator, each with advantages peculiar to specific
situations. The bucket-ladder or bucket-line dredge has been the
traditional placer-mining tool, and is still the most flexible
method where dredging conditions vary. Placer dredges, rated
according to bucket size, have ranged from 1 1/2 to 20 cubic
feet, although larger equipment has been used in harbor work.
Excavation equiment consists of a chain of tandem digging buc-
kets that travel continuously around a truss or plate-girder
ladder, scooping a load as they are forced against the mining
face while pivoting around the lower tumbler, and then dumping as
they pivot around the upper tumbler. The ladder is raised or
lowered as required by a large hoisting winch through a system of
cables and sheaves. Before the development of the deep dig-ging
dredges, the maximum angle of ladder when in its lowest digging
111-14
-------
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C
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00
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o
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60
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U.
-------
position was usually 45 below the horizontal. During the last
few years in Malaysia, 18-cubic-foot dredges digging from 130 to
158 feet below water level have often been operating at angles of
55 and sometimes more. At its upper position, the ladder
inclines about 15 below the horizontal. Figure III-3 is a side
view of the 18-cubic-foot Yuba Manufacturing . Division, Yuba
Industries, Inc., No. 110 dredge that was designed to dig 85 feet
below water level (10).
Compared with any hydraulic system, the bucket-line dredge is
more efficient in capturing values that lie on bedrock or in
scooping up the material which sloughs or falls from the under-
water face. It is more efficient when digging in hard forma-
tions, because its heavy ladder can be made to rest on the buc-
kets providing them with more ripping force. Bucket size and
speed can be varied with formation changes in the deposit
according to the volume of material that can be processed through
the gold-saving plant. Most bucket-line dredges used in placer
mining have compact gravity-system processing plants mounted on
the same hull as the excavating equipment. The waste stacking
unit, also mounted on the same hull, combines with other dredge
functions to make the dredge a complete and effi-cient mining
unit. The advantages of an integral waste dis-tributing system
trailing behind the excavator become readily apparent when
considering that up to 10,000 cubic yards of oversize waste must
be disposed of each day on a large dredge. To assure a high
percentage of running time, dredge components must be designed
for long life and relatively easy and quick replacement of parts.
111-15
-------
Dredging experience has shown that most parts need to be larger
and heavier than theoretical engineering designs indicate, and
the simpler their design, the lower their replacement and
installation costs (10).
The advantages of the bucket-line dredge as compared to the
hydraulic dredge are as follows:
1. It lifts only payload material, whereas a hydraulic system
expends considerable energy lifting water;
2. It loses fewer fines, which contain most of the fine or
small fraction gold;
3. It can dig more compact materials;
4. It can clean bedrock more efficiently;
5. It allows more positive control of the mining pattern;
6. It has a simpler waste disposal system compared to a
hydraulic system with an onshore treatment plant;
7. It requires less horsepower.
The disadvantages of mechanical systems compared to hydraulic
systems include: (1) they require more initial capital invest-
ment per unit of capacity; and (2) they require a secondary
pumping system if the excavated materials must be transferred to
a beneficiation plant which is distant from the dredge (10).
To date, a bucket-wheel excavator has not been used as part of a
mining dredge but, conceivably, if integrally designed into the
total unit, it could have distinct advantages. Bucket-wheel
control would be similar to that of a bucket line, its ladder
maneuvered vertically by a winch-cable-sheave system. Its
outstanding advantage on land, the ability to discharge directly
TII-16
-------
onto its ladder conveyor, cannot be fully utilized to dig
underwater unless the diameter of the bucket wheel is
sufficiently large with respect to the depth of the gravel and
possibly unless the bucket transfer and conveying systems are
modified. The bucket wheel would seem to have its greatest
promise on a hydraulic dredge to replace the cutterhead. With
hydraulic lift and transport, it should compare favorably with
the bucket-line system. Capable of working in either direction,
it could overcome the weakness of the cutterhead, which can
operate efficiently in only one direction, and in tough
formations it should increase output (10).
Open Cut Methods. Many perenially frozen and thawed, buried gold
placer deposits in Alaska cannot be mined profitably without
modern earthmoving equipment. In general, this equipment is used
to mine deposits where the size, depth, and characteristics of
the deposit and the topography and condition of the underlying
bedrock prohibit dredging, or where an inadequate water supply
prohibits hydraulicking. Bulldozers, draglines, and scrapers are
used in combination with hydraulic methods to mine some deposits
by open-cut methods. As indicated earlier, the choice of
excavation equipment, recovery system and the mining method is
based on the size, degree of consolidation, the physical
characteristics of the deposits, and the water supply (9, 11).
a. Bulldozers. Whether used exclusively or in combination with
other earthmoving equipment, DUO.-LUW^V.^^ aru employed in all
phases of open-cut placer mining. They are used for stripping
muck and barren gravel overburden, pushing pay dirt to
TT T_1 -7
-------
sluiceboxes, stacking tailings, and constructing ditches/ ponds,
and roads. Rippers attached to bulldozer blades may be used to
excavate bedrock where gold has penetrated fractures and joints
or frozen ground (9, 11,12). According to a Canadian study,
bulldozers are utilized at about 80 percent of Yukon Territory
placer mines (12).
The tractor sizes range from 60 to 180 horsepower, but the 150
horsepower models generally are used in mining. Straight blades
are preferred because angle blades have less load capacity.
Scrapers have limited utility but may be used in special
circumstances.
b. Draglines. Although draglines are less mobile than
bulldozers, they can move materials at a lower cost per unit.
Because of their high initial cost, however, their use is
generally limited to those operations which have large reserves
to warrant the additional expenditure for equipment. Draglines
are used essentially for the same purposes as bulldozers. The 1
1/2 cubic yard bucket capacity is preferred although the 3/4, 1,
and 2 cubic yard sizes are not uncommon (11).
Draglines are not used extensively in Alaska or in Canada's Yukon
placer industry. Draglines have been used effectively for
cleaning settling ponds (12).
c. Loaders. Front-end loaders are the second most common
equipment type and are used at about 50 percent of Yukon Terri-
tory placer mines (12). Although they are usually mounted on
111-18
-------
rubber tired wheels, they also can be track-mounted. Front-end
loaders have the following advantages (12):
(1) The economic load and carry distance may be as far
as 700 feet;
(2) Classification equipment such as grizzlies can be more
easily utilized than with bulldozers;
(3) Wheel loaders have a greater flexibility in moving
material (e.g., out of pits, around tailings piles),
Hydraulic Methods. Hydraulic mining, also known as
hydraulicking, utilizes water under pressure which is forced
through nozzles to break and transport the placer gravel to the
recovery unit (usually a sluice box). The adjustable nozzles are
also known as monitors or giants. They are also used to break up
or wash away overburden. If done in stages, frozen muck can be
thawed effectively. A pump, or occasionally, gravity is used to
produce the required pressure.
Monitors or giants can swing in a full circle and through a wide
vertical angle. The weight of the nozzle is counterbalanced by a
weight box. A giant is normally mounted on a timber or iron sled
in order to ease relocation.
The amount of material moved by hydraulic mining is measured by
cubic yards per miners inch/day (1.5 cubic feet per minute is
considered to be a miners inch). Most giants are operated under
pressure exceeding 100 pounds/square inch and use 1,700 to 50,000
gallons of water per minute.
111-19
-------
Table III-2. Estimated Monitor Discharge Rates for Various
Nozzle Sizes and Pressures (Source: Ref. 9).
Water Discharged (GPM)
Head
Nozzle Diameter (in.)
2
3
4
5
100 ft. 200 ft. 300 ft. 400 ft.
703 995
1,660 1,244
2,842 4,002
4,413 6,246
1,219 1,406
2,753 3,179
4,899 5,655
7,630 8,826
Table III-3. Typical Operating Data for Hydraulicking in the
Yukon (Source: Reference 12).
Category
Number of Giants
Nozzle Size (Diameter)
Efficient Working Pressure
Pipeline Diameter
Vol. Stripped/Unit Volume*
Wastewater Quality
a. Suspended Solids
b. Settleable Solids
Typical Values
1 to 10
2 to 6 inches
50 to 120 lb/in2
8 to 24 inches
0.8 to 1.25 yd3/!,000 gal.
(50 yd3/hr at 1,000 gpm)
270,000 mg/1 (at 1 yd3/!,000 gal.)
75 to 300 ml/1
*Efficient large-scale operation.
111-20
-------
Other Associated Activities. There are many activities which
occur at mine sites which are either directly or in-directly
related to operation of a placer mine. The remaining portions of
this subsection address these activities.
a. Prospecting and Evaluation. Sampling methods include various
types of drilling (mainly churn drilling) and excavating
(trenches pits and shafts). Other than possible erosion of
disturbed soils, sampling methods generally involve only minor
effects on water quality. However, processing of samples can in
some circumstances produce significant quantities of a sediment-
laden effluent.
Processing methods and the resultant amount of sediment produced
depend on the size of sample processed. Small samples, from a
few pounds up to a few tons, can be processed by hand with a
rocker and a pan. A steady flow of four or five gallons per
minute is sufficient to operate a small (1x4 foot) rocker. With
reuse, net consumption may be as low as 50 to 100 gallons per
cubic yard (13).
Bulk samples of up to several cubic yards can be excavated by
hand or with a tractor-mounted backhoe. These samples are
processed in a small sampling sluice 6 inches to 24 inches in
width and 6 to 20 feet in length. When working by hand, two
people can process and evaluate one to three cubic yards per day
(13). When working with a backhoe and excavating relatively
closely spaced test pits, about 100 cubic yards per day can be
111-21
-------
processed. Water requirements vary from a minimum of 50 gallons
per minute for a 6-inch sluice to several hundred gallons per
minute for a 24-inch sluice.
b. Stripping Vegetation. Mining areas are stripped for the
following purposes (12):
(1) To remove the insulating layer to allow thawing of
permafrost;
(2) To remove organic material which would interfere with
processing;
(3) To expose the overburden and mineable paydirt.
Both heavy equipment and hydraulicking are used for stripping
vegetation. Mechanical strip-ping of vegetation can expose
erodible soils and, therefore, can significantly degrade water
quality. Where stripped soils are on a slope, gully erosion can
result. Hydraulic removal of vegetation is usually a part of
hydraulic thawing and stripping overburden and can significantly
degrade water quality.
c. Thawing Permafrost. There are basically four methods of
thawing frozen ground (12):
1. Mechanical removal of the insulating layer of surface
vegetation and overburden, and solar thawing;
2. Hydraulic removal (using monitors) of the surface vegetation
and combined cold surface water and solar thawing;
3. Cold water thawing of the frozen ground by driving closely
spaced well points and injecting cold water into the thawed
ground that precedes the well point;
4. Diverting surface water over or against frozen ground
(ground sluicing).
111-22
-------
d« Stripping Overburden. In many districts, pay gravels are
overlain by silty, organic-rich deposits of barren, frozen muck
which must be removed prior to mining. Geologically, the muck is
thought to be primarily colluvium (material transported by
unconcentrated surface runoff) but may also contain loess (wind-
blown deposits). Some areas of muck are particularly noted for a
high organic and/or high ice content. Other types of overburden
are barren alluvial gravels, broken slide rock, or glacial
deposits (12). There are two primary methods of stripping used -
mechanical and hydraulic. Each will be discussed below.
Mechanical stripping referes to the use of excavating equipment
for removal of overburden. Miners who mechanically strip
overburden generally utilize the same equipment for mining. Few
have specialized stripping equipment, e.g., shovels, scrapers,
draglines, bucket wheel excavators. Mechanical stripping can be
constrained by permafrost, severe space limitations for
overburden dumps, difficult workability of weak thawing silts,
and thick overburden deposits (12).
If the hydraulicking is done in stages, frozen muck can be thawed
effectively and stripped. Pumps and occasionally gravity are
used to produce the required water pressure (12). The major
constraint to the application of hydraulicking, other than
environmental considerations, is probably lack of an adequate
water supply. Construction of storage reservoirs and lengthy
ditches and diversions are frequently necessary. Although the
water quality effects stem primarily from the hydraulicking
itself, unstable diversions, ditches, and reservoir dikes washed
111-23
-------
out by floods also contribute to the sediment load.
Processing Methods
There probably is no such thing as a single "typical" mine due to
the wide variation in processing equipment used, overburden
characteristics and methods of removal, type of deposit, size
range of the gold recovered, topography, etc. Therefore, the
actual equipment and mining methods used will probably be some
combination of mining methods and processing technology discussed
here.
Virtually all of the present placer mining operations use some
type of sluice box to perform the primary processing function,
beneficiation; but some jigs are used on dredges.
Many operations make use of feed classification. Some of the
most prominent equipment is discussed under various headings
below.
Classification. Classification (screening) involves the
physical separation of large rocks and boulders from smaller
materials such as gravel, sand, and silt or clay. The object of
classification is to prevent the processing of larger-sized
material which is unlikely to contain values. Placer miners who
were interviewed as part of a previous study reported that this
practice improves the efficiency of gold recovery (14). The
reason was attributed to the fact that a lower flow rate of water
may be required compared to the high flow rate necessary to wash
large rocks through the sluice. The low flow rate enhances the
111-24
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settling and entrapment of smaller-sized gold particles in the
sluice. Use of increased rates of flow when classification is
not practiced is thought to cause some of the finer gold
particles to be washed through the sluice and lost (14).
Operating considerations also are enhanced by preventing the
entry of large rocks and boulders which must be removed manually
when lodged in the box.
a. Grizzlies. A grizzly is a large screen of a fixed opening
size which serves to reject oversize material and prevent it from
entering the sluice. This oversize material is then discarded.
Typically, a grizzly would be inclined to ease removal of the
rejected material.
The advantage of a grizzly is that it prevents processing of
coarse material which is unlikely to contain gold, and it allows
a shallower depth of flow over the sluice riffles which enhances
recovery of fine gold. This can result in a water use reduction.
b. Trommels. A trommel is a wet-washed, revolving screen which
offers the following advantages (1):
(1) It washes the gravel clean and helps in disintegrating
gold-bearing clayey material by impact with oversize
material and strong jets of water; and
(2) It screens and distributes slimes, sand, and fine gravel
(usually less than 1/2 inch) to the processing section and
discards the oversize material.
Taggert (Reference 15) reported that plants equipped for removal
of oversize material with subsequent treatment in sluices are
capable of processing 60 to 67 percent more gravel per unit area
111-23
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of a sluice.
c. Fixed Punchplate Screen-High Pressure Wash (Ross Box). The
Ross Box is essentially a punchplate with hole sizes generally
1/2 to 3/4 inches. A dump box receives the pay gravel while a
header with several nozzles delivers wash water into the dump box
in a direction opposite to the flow of the gravel.
This turbulent washing action washes undersize material through
the punchplate where it is diverted to outside channels fitted
with riffle sections. These side channel sluices handle only
material smaller than 3/4 inch. Oversize material is washed down
the center channel which is fitted with riffles to collect coarse
nuggets (12).
d. Vibrating Screens. A vibrating screen is a screen which uses
vibration to improve the rate at which classification occurs.
Generally, 1/2 to 3/4 inch screens are used with the oversize
material rejected to a chute. These screens are loaded by a
front-end loader or a backhoe. Typically, one to four cubic
yards of material are screened at one time. In some
configurations, several size screens are stacked and different
size classifications are sluiced independently. Wet screening is
sometimes used to break up clay and loosely bound particles.
Sluices. A sluice is a long, sloped trough into which water is
directed to effect separation of gold from ore. The ore slurry
flows down the sluice and the gold, due to its relatively high
density, is trapped in riffles along the sluice. Other heavy
111-26
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minerals present in the ore are also trapped in these riffles.
These other minerals are generically called "black sands" and are
separated from the gold during final clean-up, i.e., in small
sluices, gold wheels and amalgamation.
Sluice boxes are usually constructed of steel. Typically, a
sluice is 6 to 12 meters (20 to 40 feet) long, and 61 to 122 cm
(24 to 48 inches) wide. Longer sluices are used where the ore is
not broken up prior to sluicing. Shorter and narrower sluices
are used in prospecting and during clean-up operations. Water
depths in sluices may vary from 3.8 cm to 15.2 cm (1.5 inches to
6 inches). The slope of the sluice boxes ranges from 8.3 cm to
16.6 cm vertical per meter horizontal (1 to 2 inches per foot).
The grade of sluice boxes can be varied depending upon the ore.
In general, the recovery of fine gold requires shallower and
wider sluices and steeper grades (5). The majority of the gold
is recovered in the first several feet of riffles (5).
a. Hungarian Riffles. The Hungarian riffle design is generally
considered best for use in placer mining i.4). Hungarian riffles
are essentially angle irons mounted transversely in the sluice
box as shown in Figure III-4a. The riffles are spaced 3.8 to 7.6
cm (1.5 to 3 inches) apart (4). The size and spacing of the
riffles are designed to maximize gold capture and to minimize
packing of the riffles with non-gold bearing particles. These
riffles are sometimes custom-modified with notches and holes to
improve gold recovery. The miners place carpets under the riffles
(resembling artificial turf) to capture and retain the gold for
further processing. Sections of riffles can be removed to
111-27
-------
withdraw the carpets.
b. Horizontal Pole Riffles. Wooden poles placed per-pendicular
to the flow have been used to create riffles at placer mines.
Horizontal pole riffles are sketched in Figure III-4b. This type
of riffle has been used in small-scale, remotely located
operations because the riffle can be made with locally available
materials. Wooden poles are not as durable as their steel
counterparts, and their use has largely been discontinued.
c. Longitudinal Pole Riffles. Wooden poles, usually spruce, are
placed parallel to the direction of flow through the sluice (5).
The spacing between these pole riffles varies from 3.8 cm to 7.6
cm (1.5 inches to 3 inches). Similar to horizontal pole riffles,
longitudinal pole riffles are not believed to be in widespread
use.
d. Other Riffle Types. Wooden blocks, rocks, rubber and plastic
strips, railroad rails, expended metal, heavy wire screen, and
cocoa mats have been used at various times as riffles in the
placer gold mining industry (5, 17). These riffle designs are
not in common use today.
Often undercurrents are used to withdraw a portion of the slurry
from the sluice box and re-sluice it using a different riffle
configuration. These undercurrents are usually located near the
bottom of the sluice to recover fine gold that otherwise would
remain in the tailings. Screens usually cover the entrance of
the undercurrents, and undercurrent sluices are relatively short.
111-28
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Clean-Up Methods. Many accessory heavy minerals found in the pay
gravels are also concentrated by the methods discussed in this
section. Therefore, it is essential that the concentrate
collected from the sluice is separated into gold values and the
unwanted accessory heavy minerals. The following discussion
presents methods in use today.
a. Jigs. In general, the concentrate is fed as a slurry to a
chamber in which agitation is provided by a pulsating plunger or
other such mechanism. The feed separates into layers by density
within the jig with the lighter gangue being drawn off at the top
with the water overflow, and the denser mineral (in this case
gold) drawn off on a screen on the bottom. Several jigs may be
used in series to achieve acceptable recovery and high
concentrate grade (18). In addition to clean up of concentrate
from sluices, large jigs are also used as the primary
beneficiation process to recover gold from paydirt in lieu of
sluices. Large dredges often use a number of jigs in series to
recover gold from sized or screened paydirt and at least one open
cut mine is using jigs in the primary recovery or beneficiation
of sized paydirt.
b. Tables. Shaking tables of a wide variety of designs have
found widespread use as an effective means of achieving gravity
separation of finer ore particles 0.08 mm (0.003 inch) in
diameter. Fundamentally, they are tables over which flow ore
particles suspended in water. A series of ridges or riffles
perpendicular to the water flow traps heavy particles while
111-29
-------
lighter ones are suspended and flow over the obstacles with the
water stream. The heavy particles move along the ridges to the
edge of the table and are collected as concentrates (heads) while
the light material which follows the water flow is generally a
waste stream (tails). Between these streams may be some material
(middlings) which has been partially diverted by the riffles.
These are often collected separately and returned to the table
feed. Reprocessing of heads or tails, or both, and multiple-
stage tabling are common.
c. Spirals. Spiral separators i.e., Humphrey concentrators,
provide an efficient means of gravity separation for large
volumes of material between 0.1 mm and 2 mm (0.004 to 0.08 in) in
diameter. Spirals have been widely applied, particularly in the
processing of heavy sands for titanium minerals (19). Spirals
consist of a helical conduit (usually of five turns) about a
vertical axis. The ore, or in this case concentrate, is fed to
the conduit at the top and flows down the spiral under gravity.
The heavy minerals concentrate along the inner edge of the spiral
from which they may be withdrawn through a series of ports.
Wash-water may also be added through ports along the inner edge
to improve the separation efficiency. In large plants, several
to hundreds of spirals may be run in parallel, although in placer
mining operations, a small number is usually sufficient. At
least one dredge and one open cut mine have been reported as
using spirals in the primary recovery of gold from placer
deposits.
111-30
-------
d. Gold Wheels. A gold wheel is a gravity separation device
used during cleanup to separate the gold from the "black sand."
The wheel may vary between 30 cm to 112 cm (12 inches to 44
inches) in diameter and may rotate at a rate up to 42 rpm. The
rotational speed can be controlled by the operator. Inside the
wheel, there are 0.64 cm (1/4 inch) to 1.27 cm (1/2 inch)
channels arranged in a helix. The wheel is tilted with only
small angles being capable of separating materials of relatively
different specific gravities. Conversely, steeper angles
separate materials with little difference in specific gravity.
Water is sprayed onto the wheel from several ports at a rate of
10 gpm or less. This water can be recirculated if needed. Gold
concentrate is placed along the perimeter of the wheel, and the
gold works its way to the center where it is withdrawn. The
lighter material flows over the perimeter of the wheel and is
captured and reworked to recover any remaining gold. Sur-
factants (e.g., soap) are sometimes added to the water to aid in
directing flow of the gold to the center.
e- Small Sluices. Small sluices are simply scaled-down versions
of the sluices described above. The advantage of using a small
sluice is that only small amounts of concentrate are processed at
a rate conducive to maximize gold separation from other heavy
minerals in the concentrate. Several passes or several small
sluices may be used in series to ensure that no gold is lost.
Only small amounts of water are required because the size range
of the concentrate is relatively restricted.
111-31
-------
f. Magnetic Methods. A large proportion of the heavy mineral
concentrate from which the gold is extracted may contain minerals
(primarily magnetite) which exhibit magnetic prop-erties. The
basic process involves the transport of the concentrate through a
region of high magnetic field gradient. In large-scale
applications of this method, an electromagnet may be used, but at
small operations, a hand magnet is often em-ployed. This method
is often applied along with other methods to effect the best
separation of the gold from other heavy minerals in the
concentrate.
g. Chemical Methods. There are two chemical methods in use in
the gold industry today which may be used in association with
gold placer mining: amalgamation and cyanidation. Amalgamation
was used on a wider scale in the past but is not commonly used
today except for cleanup of a concentrate. Cyanidation is not
known to be used for extraction of gold from a concentrate but
could be used to rework tailings from placer operations by heap
leaching. This guideline does not cover wastewater from such
methods.
1. Amalgamation. Amalgamation is the process by which mercury
is alloyed, generally to gold or silver, to produce an amalgam.
The amalgam is placed in a small retort to recover the mercury
for reuse and to reclaim the gold. However, since placer gold
can be purchased directly for jewelry, mercury is seldom used.
This is because after amalgamation, it must be retorted. This
reduces its value because the gold is tarnished and often welded
together (9). An amalgamator, which would be a cylinder of some
rn-32
-------
type (even a small cement mixer would do) is turned either
manually or mechanically. Mercury is introduced with the
concentrate and becomes amalgamated with the gold. The amalgam
is then retorted and the mercury recovered.
2. Cyanidation. The use of this process is unknown in Alaska
for primary extraction of placer gold but has been used elsewhere
to recover gold from low grade ores by heap or vat leaching. It
has been economically applied in the recovery of gold from
tailings left by hard rock gold mills. The cyanidation process
involves the extraction of gold or silver from fine-grained or
crushed ores, tailings, low grade mine rock, etc., by the use of
potassium or sodium cyanide in dilute, weakly alkaline solutions.
After dissolution of the gold, the gold is absorbed onto
activated carbon or precipitated with metallic zinc. The gold
may be recovered by filtering with the filtrate being returned to
the leaching solution. A more complete description of this
process may be found in Reference 18.
Small-Scale Methods. The methods described in this sub-section
are primarily utilized by recreational or asseessment operations.
The various small-scale methods are similar to regular methods
in that they employ principles based upon gravity separation.
Small-scale methods are responsible for only a very small
percentage of all placer gold production. A few representative
methods are described below.
a« Gold Pan and Batea. Panning currently is mostly used for
prospecting and recovering valuable material from concen-trates.
111-33
-------
The pan is a circular metal dish that varies in diameter from six
to eighteen inches with sixteen-inch pans being quite common.
The pans often are two to three inches deep and have 30- to 40-
degree sloping sides. The pan with the mineral-bearing gravel or
sand is immersed in water, shaken to cause the heavy material to
settle toward the bottom of the pan, and then the light material
is washed away by swirling and overflownig water. This is
repeated until only the heavy con-centrates remain. In some
countries, a conical-shaped wood pan, called a batea, is used.
This unit has a 12- to 30-inch diameter with a 150-degree apex
angle. It is often used to recover valuable metals from river
channels and bars.
b. Long Tom. A long torn is essentially a small sluice box with
various combinations of riffles, matting, expanded metal screens,
and occasionally amalgamating plates. A long torn usually has a
greater capacity than a rocker box and does not require the labor
of rocking. It consists of a short receiving launder, an open
washing box six to twelve feet long with the lower end a
perforated plate or screen set at an angle, and a short sluice
with riffles. The component boxes are usually set on slopes
ranging from one to one and one-half inches per foot.
c. Rocker Box. Rocker boxes are used to sample placer deposits
or to mine high-grade areas when installation of larger equipment
is not justified. The box is constructed of wood and is
essentially a short, sloped box chute over which the pay dirt and
water flow as the box is rocked back and forth. A screen is
111-34
-------
mounted at the head of the box to reject oversize material. It
may be fitted with riffles and usually has a canvas bottom.
d. Dip Box. The dip box is useful where water is scarce and
where an ordinary sluice cannot be used because of the terrain.
It is portable and has about the same capacity as the rocker box.
The box is about six to twelve feet long, and twelve inches wide
with six-inch sides. The bottom of the box is covered with
burlap, canvas, or thin carpet to catch the gold. Over this is
laid a one-by-three-foot strip of heavy wire screen of about 1/4-
inch mesh. Material is dumped or shoveled into the upper end and
washed by pouring water over it from a dipper, bucket, hose, or
pipe until it passes through the box. Large rocks are removed by
hand and riffles may be added to the lower section of the box to
improve recovery (17).
e. Suction Dredge. Small suction dredges have been used
successfully while prospecting or for recreational or small
(part-time) ventures. The pump sizes most commonly found in use
vary from one to four inches. The pump is usually floated
immediately above the area being worked. There are two basic
assemblies that are commonly used: (1) the gold-saving device is
in a box next to the suction pipe and carried under water, and
(2) the other system uses two hoses in the nozzle - one
transporting water to the head and the other transporting
material to the surface of a gold-saving device (9).
INDUSTRY PRACTICE
Until recently, little detailed information was available con-
111-35
-------
cerning placer mining operations in Alaska and other states.
However, during the last few years, EPA has embarked upon efforts
described elsewhere in this document to identify specific
operations and obtain information concerning mining practices,
wastewater treatment technologies employed/ flow, etc. This
information has been obtained by site and sampling visits, review
of tri-agency report forms, visits to state pollution control
agencies, and from other sources.
The objective of Table III-4 to Table III-8 is to provide
information and data gathered at mining operations in this
industry subcategory. Discussion of an operation or presentation
of data and information does not imply that the mining operation
is exemplary, typical, or represents good wastewater treatment.
This list does not include all existing mines, particularly with
respect to the hundreds of recreational or assessment operations
which are known to exist. Rather, the tables that follow present
a summary of data and information that EPA has obtained which
serve to illustrate the range of opera-tions in the United States
today.
Some characteristics of the operations emerge from examination of
the information gathered, however, which serve to place the gold
placer mining industry in perspective. Most operations are
located in remote areas far from supplies and the amenities of
civilization. Many operations are family-owned and operated and
probably over 95 percent employ seven (or fewer) persons. Most
of the operations are seasonal generally averaging between 100 to
115 operating days per year. The size of the operations ranges
111-36
-------
from processing less than 20 cubic yards per day to as much as
12,000 cubic yards per day (10). Although gold is very valuable,
the amount contained in the paydirt is very low with even the
richest deposits containing only a few grams of gold per cubic
yard; the gold gives a value of a few cents to over eight dollars
per cubic yard of pay dirt and more depending upon the current
international price for gold.
Wastewater treatment technology employed in the industry gen-
erally ranges from no treatment to settling ponds and discharge
or to recycle of wastewater. The majority of mines provide some
settling, and a few employ tailings filtration for solids
removal. No advanced treatment technology or chemical methods
are known to be employed in Alaskan operations today although
some operators have tried flocculant addition in the lower 48
states. Recycle ranges from nonexistent to 100 percent, but at
most operations recycle is employed primarily to conserve water
and occurs only intermittently. Electric power is usually
generated on-site by the operators with fuel delivered
periodically to the site, often by air.
The remainder of this section consists of Tables III-4, III-5,
III-6, III-7, and III-8 which are profiles of the Alaska,
California, Colorado, Idaho, and Montana gold placer mines
surveyed and for which some data were available. Although
limited production has been reported from other states, we have
no precise data on the number of mines or production in other
states. Figure III-4 gives the locations for the various mining
districts in Alaska.
111-37
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REFERENCES
1. Alaska Office of Mineral Development, "Alaska's Mineral
Indstry - 1982," Special Report 31, 1983.
2. Mineral Facts and Problems, 1980 Edition, U.S. Bureau
of Mines Bull. 671.
3. USEPA-Region X, "Draft General NPDES Permit for Placer
Mining in the State of Alaska," February 14, 1983.
4. U. S. Geological Survey, United S_ta_te_s MjLnejral
Resources (Gold), U.S.G.S, Professional Paper 820, 1973,
p. 263-275.
5. Wimmler, N. L., "Placer Mining. Methods and Costs in
Alaska," U. S. Department of Commerce, Bureau of Mines,
Bulletin No. 259, p. 10-15, 1927.
6. Jackson, C. F., "Small-Scale Placer Mining Methods," U.S.
Department of Interior, Bureau of Mines Information
Circular 1C 6611R, February 1983, p. 15-18.
7. Louis Berger and Associates, "The Role of Placer Mining in
the Alaska Economy," prepared for the State of Alaska
Department of Commerce and Economic Development, March
1983.
8. U. S. Department of the Interior, Minerals Yearbook -
Preprint "Gold" 1982, U. S. Bureau of Mines (Author j. M.
Lucas) Report No. 1804-1, October 20, 1980.
9. Alaska Department of Environmental Conservation, "Placer
Mining/Water Quality - Problem Description," Alaska Water
Quality Management Planning Program Section 208 Study
(P.L. 92-500), November 1977.
10. Romanowitz, C. M., Bennett, and Dare, W. L., "Gold Placer
Mining - Placer Evaluation and Dredge Selection," U. S.
Bureau of Mines Information Circular 8462, 1970.
11. Thomas, B. I., Cook, D. J., Wolff, E., and Kerns, W. H.,
"Placer Mining in Alaska - Methods and Costs at Operations
Using Hydraulic and Mechanical Excavation Equipment with
Nonfloating Washing Plants," U. S. Bureau of Mines
Information Circular 7926, 1959.
12. Sigma Resources Consultants, Limited, "Water Use Technology
for Placer Mining Effluent Control," Department of Indian
and Northern Affairs, Canada, Report No. QS-Y006-000-EE-A1,
Whitehorse, Yukon Terr., 1981.
13. Wells, J. H., "Placer Examination, Principles and
111-39
-------
Practice," U. S. Bureau of Land Management, U. S.
Department of Interior, 1969.
14. Bainbridge, K. L., "Evaluation of Wastewater Treatment
Practices Employed at Alaskan Gold Placer Mining
Operations," Calspan Corporation Report No. 6332-M-2,
July 17, 1979.
15. Taggert, A. F., Handbook of_ Mineral Dressing, John
Wiley, New York, 1945.
16. Lapedes, D. N. (ed), McGraw-Hill Encyclopedia of
Environmental Science, 1974, p. 342-346.
17. West, J. M., "How to Mine and Prospect for Placer Gold,"
U. S. Department of the Interior, Bureau of Mines
Information Circular No. 8517, 1971.
18. USEPA, "Final Development Document of Effluent Limitations and
Standards for the Ore Mining and Dressing Point. Source
Category," EPA Report 440/1-82/061, November 1982.
19. Harty, D. M. and Terlecky, P. M., "Titanium Sand Dredging
Wastewater Treatment Practices," Frontier Technical
Associates, Inc., Report No. 1804-1, October 20, 1980.
111-40
-------
SECTION IV
INDUSTRY SUBCATEGORIZATION
During development of effluent limitations and new source
standards of performance for the ore mining and dressing category
in 1982, consideration was given to whether uniform and equitable
guidelines could be applied to the industry as a whole, or
whether different limitations and standards ought to be
established for various subparts of the industry. The ore
mining and dressing industry was subdivided into eleven
subcategories or subparts based primarily upon ore type. The
subcategories were further subdivided into subdivisions:
discharges from mines (mine drainage) and discharges from mill or
beneficiation processes. Currently, placer gold mining is
included in Subpart J, Copper, Lead, Zinc, Gold, Silver, and
Molybdenum Ores Subcategory of the final subcategorization scheme
promulgated in 1982 for the Ore Mining and Dressing Point Source
Category. In this notice, EPA is proposing to designate placer
mining as a separate subcategory because the placer deposits and
extraction techniques are significantly different than those
covered under Subpart J.
In developing this proposed placer mining regulation, EPA
considered whether further subcategorization of the placer mining
industry was necessary. Like many types of mining, placer
operations are conducted as land surface activities with
resultant water pollution problems that are affected by variable
influences such as size of the operation, climate, topography,
IV-1
-------
mining and wastewater control practices and other factors.
Unlike many other segments of the ore mining industry, placer
operations are often located directly within the bed of the
stream or river to which the solid and wastewater effluents are
also discharged.
Similar to those originally identified for the ore mining and
dressing industry, the following specific factors were used by
the Agency to review the technical aspects of gold placer mines.
1. Size
2. Mining Method
3. Ore Processing Method (including Classification)
4. Treatability of Pollutants (including mineralogy of the ore
and overburden)
5. Topography and Geographic Location
6. Treatment/Control Techniques (including Recycle)
7. Climate and Rainfall
8. Water Use or Water Balance
9, Solid Waste Generation
10. Number of Employees
11. Energy Requirements
12. Reagent Use
13. Age of Facility
A comprehensive analysis of the above listed technical
considerations reveals there is justification for further
subcategorization of the placer mining industry. A detailed
discussion of each of these factors is presented below.
IV-2
-------
Size (Capacity to Process Ore)
An industry profile demonstrates a convenient and rational means
to divide the industry on the basis of size (capacity to mine, or
through-put, calculated as cubic yards per day of paydirt
processed), which is closely related to mining method (to be
discussed later). One conceptual division is based on whether a
facility is "non-commercial" or"commercial" (i.e. small capacity
versus large capacity). The non-commercial (recreational, hobby
and assessment types of operations) tend to be very small, while
the commercial operations vary in size from fairly small to very
large. The non-commercial mines or operators may number over
1000 and be the largest percentage of the industry both in Alaska
and in the contiguous 48 states. However, EPA has been unable to
obtain any variable data on the number and location of these very
small operations as discussed below. For purposes of this
proposed regulation, we have define "non-commercial" as mines
that process less than 20 cubic yards of ore per day. Because
they process a low total volume of ore, they generally discharge
a very low volume of process water. These small mines
characteristically have little mechanized equipment, and are
usually intermittent in operation. They include weekend panners,
small suction dredges, small sluices, and rocker box operations.
Table IV-1 is a partial profile of small gold mines. The
assessment group includes those operations that could develop a
commercial or larger type of operation, but for one of several
reasons, is doing only a limited amount of work adequate to
maintain legal control of their property. This group also covers
IV-3
-------
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IV-3 a
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prospecting, testing, and development work.
This proposal designates all mining operations that process or
handle less than 20 cubic yards of pay dirt per day as "small
recreational/assessment (non-commercial mines)."
Commercial gold placer mines vary in size from 20 cubic yards per
day (generally somewhat more to be truly commercial) to many
thousands of cubic yards per day processed by the largest
dredges. As mentioned above, many factors influence the ultimate
size of a placer mine. Examination of the available data base
shows another means to delineate a group of mines by size and
mining method which also have other features in common. This type
of mine is characterized by its very large size, use of dredging
technology, and extensive use of recycle (approaching 100
percent). Table IV-2 is a partial summary of industry facilities
processing 4,000 cubic yards or more of pay dirt per day by
dredging methods. Based upon the size and mining method
characteristics of this group, they have been subcategorized as
the "large dredging" segment. The dredging technique is
discussed in detail in Section III, "Industry Profile."
A large group of mines remains between the two segments discussed
above. These are larger than 20 cubic yards per day and
encompass all mining methods except dredges processing in excess
of 4,000 cubic yards per day. These facilities generally use
similar mining and processing methods, have similar constraints
and limitations placed upon their operations, and have similar
wastewater problems.
IV-4
-------
Table IV-3 illustrates the percentage small, non-commercial mines
versus larger, commercial mining ventures by location (Alaska vs.
Lower 48).
Table IV-2. Dredge Placer Mines Having Production Greater
Than 4,000 yd3/day1
Mine
4126
4127
4211
4260
Production
(yd3/day)
20 yd3/Day
Commercial
Total
Alaska
Lower 48
States
400 + 2
1,400 + x
300 +2
230-2503
700 +
1,250 +
Total
1,400
550 +
1,950
^Source - EPA Estimate
2Source is a review of Alaskan Tri-State Agency Permits,
plus a review of EPA NPDES permit applications
^Source - a review of State Agencies in the following
states: California, Colorado, Idaho, Montana, Nevada,
Oregon, Washington
IV-5
-------
Figures IV-1 and IV-2 are plots of production versus percentage
of mines in each production interval for Alaska (separately on
Figure IV-1) and California, Colorado, Idaho, and Montana (shown
as a group on Figure IV-2). These data show the same general
distribution by size for the two areas. There are several minor
differences between these two general areas of location of the
industry; harsher climatic conditions, shorter length of
operating season, the availability of water, and slightly higher
costs to operate prevail in Alaska.
EPA has concluded that the many similarities in the mines of
Alaska and the contiguous 48 states are compelling; none of the
above-mentioned differences are of such significance as to
warrant subcategorizaton on this geographical basis.
EPA believes size is an appropriate criterion for
subcategorization because many of the differences between mines
are directly related to size. Principal among these are the
mining and ore processing methods employed, mass of pollutants
discharged in the wastewater, and economic viability of the mine.
Mining Method Employed
There are two general mining methods being employed in the
industry today - mechanical and hydraulic. The choice of mining
method is determined by the general geology, grade of ore
(assay), size, configuration and depth of the deposit, type and
thickness of overburden, geographic details of the site, and
availability of water. The mechanical approach to mining
IV-6
-------
Figure IV-1. Distribution of Alaska Placer Gold Mines by
Size (Source: Computer Summary of Tri-Agency
Forms - 1983).
30
28
26
24
22
20
18
16
14
fel2
h- 10
••^•^
01
2
0
HL
PRODUCTION (CUBIC Y'fiRDS PER DRV)
KFi MINES DISTRIBUTION BY SIz
IV-6a
-------
Figure IV-2. Distribution of Placer Mines in the Lower
48 States by Size (source: Permit Files
from Montana, Idaho, Colorado, and California)
PRODUCTION (CUBIC YfiRDS PER DRY)
LOWER 48 DISTRIBUTION BY SIZE
IV-6b
-------
utilizes little or no water in the method. With the advent and
adaptation of the small, high powered diesel engines to
tractors, loaders, shovels, draglines, backhoes, and vehicles,
the miner is able to move mechanically larger volumes of material
(ore and waste) economically, thus significantly expanding this
segment of the industry. A 200- to 400-horsepower diesel tractor
has the capability to rip, strip, move, stockpile, or feed 3,000
to 6,000 cubic yards daily. The mines employs a surface, open-
cut method.
Another mining method in current use that is classified as
mechanical mining is the use of mechanical buckets in dredging
operations. The ore is cut, mined, and moved mechanically in
buckets attached to a continuous chain. The dredge has a self
contained method to process the ore (See Section III) and to
dispose of the waste material. As presented under the "Size"
section above, the very large dredge processing in excess of
4,000 cubic yards per day of paydirt is one of the proposed
segments of subcategorization. This subcategorization is based
on both size and utilizaion of a unique mining method. (See
Section III, "Industry Profile").
The hydraulic system of mining uses varying amounts of water,
i.e., small suction dredges often use less than 10 GPM and large
hydraulic water canons can use over 10,000 GPM. The small
suction dredges are often used in the non-commercial category by
hobbyist. A few large suction dredge operations have existed in
the past, but due to inefficiencies in operation and depth
restrictions these have been (or are being) replaced by
IV-7
-------
mechanical dredges. The hydraulic water canon mining technique,
although still in use is being replaced by mechanical means. The
hydraulic system, if used to clear or move overburden, utilizes a
large volume of water and generates a large volume of pollutants
in the wastewater. The hydraulic system can also be used to thaw
overburden but is very water use-intensive. The smaller
hydraulic canons are being used to load ore into the sluices, for
mixing purposes and for the movement of wastes. Regardless of
the mining method employed, the processing of pay dirt generally
employs similar gravity and physical separation methods to
produce a concentrate (See Section III). Thus the very large
dredge is segmented as a subcategory on the basis of size and
unique mining method with limited or no discharge of wastewater.
Since differences in mining method in general (other than the
very large dredge) track the proposed scheme of subcategorizaton
by size (capacity) it has not been proposed as a separate basis
of subcategorization.
Ore Processing Methods (Including Classification)
The gold placer mining industry currently utilizes several
gravity and physical separation methods to process ore and
recover the free gold. As mentioned previously, the scope of
this rulemaking proposal is limited to this particular type of
ore processing. Currently, the industry in all areas of the
country utilizes straight sluicing, sluices with punch plates and
undercurrents, sluices with varying degrees of classification,
jigs, spirals, cyclones, and tables (See Section III) to produce
IV-8
-------
gold. Although physical classification of the ore by particle
size is considered a part of ore processing, it was also examined
as a potential discrete basis for subcategorization. The various
methods of classification all reach the same result - reduced
volume of ore to process by separating a portion(s) by particle
size into a direct waste component (gangue or tailings) which
reduces the total amount of water needed to process the ore and
therefore, reduces the wastewater to the treatment system or
receiving stream. (See "Placer Mining Wastewater Treatment
Technology Project, Phase 3 Final Report - Draft, January 1985 by
Shannon & Williams, Inc.)-" The total tonnage of particulate
matter in the wastewater effluent is reduced by the amount
classified out of the ore (See Section III for types of
classification). Based on the wide variations in type and degree
of classification utilized, plus the fact there is no fundamental
difference in the type of pollutants produced with or without
classification, the Agency is not proposing classification as a
means of subcategorization.
Treatability (mineralogy of the ore and overburden)
The gold placer mining industry generates wastewater that is
relatively consistent in the types of pollutant ("muddy water"
subject to variation in composition from different sources),
while the quantity of pollutants found in the wastewater varies
considerably. The amount of pollutants depends on several
factors in addition to the size of operation. The mineralogy of
the waste rock and soil involved, amount of classification used,
and the degree of recycle or treatment employed bear directly
IV-9
-------
upon the quantity of pollutants produced and discharged to the
environment.
The mineralogy of an ore deposit often determines the recovery
(beneficiation) process to be used (See Section III).
Consideration must be given to both the valuable portion (free
gold in this case) and the waste (gangue) portion of the "pay
dirt." Placer deposits are either alluvial or glacial in origin
(See Section III). The alluvial deposits generally concentrate
the heavier portions of the "pay dirt," while glacial action
tends to scatter all segments of the deposit on a random basis.
Both types produce a wide range of particle shapes and sizes, and
particle composition varies by the original source of the
material. The miner has no control over particle size and
distribution or composition (colloidal matter) in the deposit,
but all of these factors directly affect the treatability of the
effluent. Settling rates for the particles vary by size, shape,
and composition (specific gravity). In addition, if the particle
is colloidal (in addition to small in size) the electromagnetic
forces involved tend to keep these particles in suspension for a
longer period of time. However, treatment options considered (see
Section VIII) may overcome this difficulty by application of
settling aids which cause the fine particles to coagulate and
thus settle out sooner. The wide range of particle size,
distribution, and composition possible in these ores make it
impossible to use treatability or mineralogy as a basis for
subcategorization. This is an area where additional work could be
done.
IV-10
-------
Topography and Geographic Location
As discussed in Section III, "Industry Profile," and in other
areas of this section, there are more than 700 placer operations
in Alaska and as many as 1,300 mines in the 48 contiguous states
(non-commercial and commercial) with the vast majority located in
seven western states (California, Colorado, Idaho, Montana,
Nevada, Oregon, and Washington). The majority of site-specific
information the Agency has is representative of mines in Alaska.
Topography differs between mining areas and from site to site
within areas (i.e., seashore marine gravels to broad, gently
sloping valleys to rugged, narrow, steeply sloping valleys).
These differences can affect the operation, particularly as
regards waste disposal and settling pond location and size.
Rainfall accumulation and runoff from steep slopes can cause
problems as well. Narrow valleys with steep slopes place
constraints upon the location of ponds in terms of area available
(or whether it can even be built), construction costs, and the
costs associated with pumping against a greater head for recycle.
Topography has an impact on construction and cost of operation.
However, based on the current data available to the Agency,
topography does not significantly affect wastewater
characteristics or treatability, and thus is not proposed as a
basis for subcategorization at this time.
IV-11
-------
Regardless of the geographic location, the industry members have
similar problems regarding wastes (both liquid and solids).
Logistics, operation, and communications problems are enhanced in
the more remote areas but these do not affect the quantity or
quality of the effluent wastewater from a given operation. There
is a wide range of site specific conditions present throughout
the industry, but as also discussed under size or capacity to
process ore, the similarities in mines regardless of geographic
location is significant. Therefore, geographic location is not
proposed as a basis for subcategorization.
Treatment and Control Technologies
Currently the gold placer mining industry practices one type of
end of pipe wastewater treatment and control technology: settling
pond(s) (either single or multiple in series) and either with or
without recycle. There are a number of variations in site
specific layouts. Pond efficiencies can be enhanced if a bypass
diversion channel is incorporated in all sites as a standard
design item.
This diversion would serve several purposes:
1) Separate normal stream flow from the treatment system, thus
reducing the load on the pond(s) and increasing settling capacity
and efficiency.
2) Provide relatively good quality water for dilution purposes
with plant effluent at end-of-pipe discharge prior to final
effluent sampling point.
IV-12
-------
3) Provide an inplace storm flow runoff facility to minimize
chances of filling the ponds with extraneous material or
breaching the pond berms and thus allowing excessive wastewater
discharge to the stream system.
The effectiveness of settling due to varying operating and
maintenance practices covers the full range from nil to quite
good. Classification of the ore prior to sluicing allows for a
reduction in the amount of water required to process that same
amount of raw ore as discussed above.
Recycle of the process water stream is the most effective method
of operation to reduce the pollutants going to the stream system.
High rate recycle is currently employed in the industry,
particularly by dredges and sites that are water short. A number
of mine sites have adequate process water (without recycle) in
the early part of the season, but as the summer progresses the
surface water deminishes and recycle is employed on an as
required basis. The Agency has been told that recycle with
subsequent increases in total suspended solids in the wash water
reduces the recovery of fine gold. Recent tests have shown that
recycle, within the limits of pilot demonstration, does not
adversely affect fine gold recovery. (See Section VIII). More
work is needed in this area and the Agency invites comments on
this subject. While there are some exceptions in degree, all of
the treatment technologies discussed are generally applicable
regardless of type, size, location and all other factors.
IV-13
-------
Accordingly, since the applicable technologies for all types and
configurations of placer mines are similar, it is unnecessary to
subcategorize on this basis.
Climate and Rainfall
There is a wide diversity of climatic and rainfall conditions in
the locations where placer mines are operated. Unlike a number
of other industries, placer mine operators cannot choose a
location with more favorable climate or rainfall conditions, but
must accommodate whatever is present at the discovery site. Some
mines are located in regions close to the coast and as a result
have milder climate and more abundant rainfall, which in turn
allows for a longer mining season with fewer problems as relates
to availability of process water. Other mines are located in
interior areas including mountainous terrain with resultant
colder, harsher climates and possibly reduced rainfall for part
of the operating season. These areas have shorter mining
seasons, and may have to contend with permafrost and a shortage
of water. Some of these areas are fed by glacial meltwater,
which compensates for the lack of adequate rainfall.
Although climate and rainfall have a direct bearing on the length
of mining season, to some degree on the types of mining and
recovery processes used, occurrence of pernteifrost, and
availability of process water (possibly necessitating recycle)
they do not control the size of mining operation, the quality or
quantity of wastewater (except as it affects the degree of
recycle employed), or the treatment technology used. Therefore,
IV-14
-------
these factors are not proposed as a basis for subcategorization.
Water Use o£ Water Balance
Water use or water balance is directly controlled by the mining
method, the recovery process employed and is site specific. The
type of deposit, type and amount of overburden, water
availability, climate and rainfall or geographic location affect
the water use or water balance. Due to the extreme variability
of all the factors involved plus the fact that waste
characteristics are essentially constant (subject to degree of
recycle for mechanical operations and dredge operation
methodology), the Agency is not proposing subcategorization of
this segment by water use or water balance.
Solid Waste Generation
Physical and chemical characteristics of solid waste generated by
treatment of gold placer mining wastewater are determined by the
paydirt and overburden characteristics. These are beyond the
control of the operator and are site specific. The miner
recovers a fraction of a percent of the material mined (less than
a fraction of an ounce per ton mined). The majority of the solids
removed in the beneficiation process simply fall out in front of
the sluice before wastewater treatment. The characteristics of
the solid waste generated by wastewater treatment are unrelated
to differences in currently employed mining and process
technology with the exception of total recycle in both mechanical
and dredge operations (i.e., zero discharge). Current wastewater
process technology is virtually identical in this segment
IV-15
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(settling ponds) for all types of mining operations. Therefore,
this factor is not a basis for subcategorization.
Number of Employees
The amount and quality of process wastewater generated is
directly related to the size (through-put capacity), the mining
and recovery processes employed, the amount of water available,
the degree of recycle employed, the effectiveness wastewater
treatment employed, plus the site-specific factors related to
each individual mine (i.e., treatability, mineralogy, location,
topography, geology, overburden and paydirt characteristics,
etc.). A larger mine requires more people for its operation, so
there is a correlation between number of employees and the size
factor considered above.
Energy Requirements
Energy requirements in this segment vary widely. The main use of
energy in wastewater control and treatment is for pumping recycle
water when recycle is required. However, this energy requirement
would be only a slight increase over the energy presently
required to supply process water at mines pumping wash water to
the beneficiation process. Energy for pond construction and
maintenance is only a small fraction of the energy required for
mining and processing. It is very difficult to reliably identify
energy requirements specifically related to wastewater treatment.
Therefore energy requirements is not selected as a basis for
subcategorization.
IV-16
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Reagent Use
Current operations for which the Agency has information do not
use reagents to recover free gold in the gold placer industry.
Mercury coated copper recovery plates located in the flow stream
at the end of the sluices have been employed in the past but seem
to have lost their appeal in the current operating schemes. None
were observed during the last several years of site visits by the
Agency. In addition, this subcategory (gold placer mines) is
limited in scope to include only physical and gravity separation
(recovery) methods. Thus the use of reagents would be covered
under the existing regulation for the ore mining and dressing
point source category at 40 CPR Part 440, Subpart J.
Facility Age
Many placer mines have been operated in the same general location
in excess of 50 years (usually under different management). A
number of these deposits have been reworked several times to
recover gold which was jnissed by previous operators for one of
several reasons (i.e., inefficiencies in the operation,
oversight by the operator, or extension of the deposit in depth
or area). Mining equipment and processing equipment (sluices)
are repaired or replaced as needed. The same operating
techniques and wastewater treatment systems applicable to this
industry may be employed at old or new mines or at new locations
within an existing operation as required without consideration of
the age of the facility. Therefore age of the operation is not a
useful basis of subcategorization.
IV-17
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Subcategorization Based on the Technical Aspects of Gold Placer
Mines
Table IV-4 is a summary of the Subcategorization for the gold
placer mining industry based upon technical consideration. This
scheme employs the size and mining method as the basis for
Subcategorization. It is recommended that no limitations be
proposed for small operations (recreational/assessment)
processing less than 20 cubic yards per day as discussed in this
section. Dredging offshore, coastal zone (beach placers) or
within river operations are not included in the proposed
regulation due to lack of data.
Table IV-4. Subcategorization for Gold Placer Mines Based on
Technical Consideration
Process Rate (yd3/Day)
Small Mines (All Methods) <20
Intermediate Mines (All Mining >20
Methods)
Very Large Dredges >4,000
Economic Considerations
EPA's economic assessment of the proposed regulation is presented
in the "Economic Analysis of Proposed Effluent Limitations and
Standards for the Gold Placer Mining Industry." This report
estimates the required investment and annual costs for existing
sources in the industry as a whole and for typical new sources
IV-18
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covered by the proposed regulation. Compliance costs are based
on engineering estimates of capital requirements and construction
expenses as set forth in Section IX of this document. These
estimates include the full cost for settling ponds and/or recycle
equipment at mine sites, since accurate, mine-specific
information on treatment-in-place is unavailable. The economic
analyses also estimates the impacts of the costs of the
regulation, price changes, production changes, profitability
changes, mine shut-downs, employment changes, local community
impacts, balance of trade effects, and industry structure
changes.
The analysis indicates that mines processing less than 50
yd^/hr, 10 hours per day, i.e., 500 yd3/day are generally
not viable operations and are projected to be unprofitable in the
baseline.
Although no exact determination can be made, EPA's analysis
indicates a miner's potential for earning a profit increases as
the size of the operation approaches and exceeds 500 yds3
processed per day. The Agency has therefore chosen this level of
production as a boundary or cut-off. Just as most mines below
this size level are projected to be unprofitable, most mines
above this size level are projected to be financially healthy.
The Agency has subcategorized to reflect the differential impacts
for mines of a size that processes less than 500 yd3/day of
paydirt as summarized in Table IV-5.
IV-19
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Table IV-5. Proposed Subcategorization for Gold Placer Mines
Process Rate (yd3/day)
Small Mines (All Methods) <20
All Mines (All Methods) >20 and <500
All Mines (All Methods except >500
large dredges)
Large Dredges >4000
IV-20
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SECTION V
SAMPLING AND ANALYSIS METHODS
GENERAL
The sampling and analysis program discussed in this section was
undertaken primarily to develop a data base for proposal of
effluent limitations and standards for placer mining, to support
EPA Region X in acquiring data to develop NPDES permit conditions
and to identify pollutants of concern in the industry, with
emphasis on suspended and settleable solids, turbidity, and toxic
metals (particularly arsenic and mercury). A data base has been
developed over several years based on sampling and analysis
programs from which the data have been drawn. A listing of these
programs is presented below:
1. Treatability Studies—1984; Kohlmann Ruggiero Engineers
(KRE)
2. Reconnaissance Study—1984; KRE
3. Reconnaissance Study—1984; EPA Region X
4. Reconnaissance Study—1984; Frontier Technical Associates
(FTA) (Lower 48)
5. Wastewater Treatment Technology Project; Shannon and
Wilson
6. Treatability Studies— 1983; FTA and KRE
7. Reconnaissance Study—1983; FTA and KRE
8. Reconnaissance Study—1983; EPA Region X
9. Reconnaissance Study—1982; EPA Region X
V-l
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10. Environment Canada—1983 Yukon Study
11. Canadian Department of Indian and Northern Affairs—1981
Yukon Study
12. R&M Consultants—1982 Treatability Study, Site Visits and
Pond Design Manual (for ADEC)
13. Calspan Corporation—1979 Reconnaissance Study
14. Alaska Department of Environmental Conservation—1977,
1978, and 1979 Reports
15. EPA-National Enforcement Investigations Center—1977
Reconnaissance Study
16. Dames & Moore—1976 Reconnaissance Study (for Calspan)
This section identifies the sites sampled and parameters analyzed
for the EPA and contractor studies for 1984, 1983 and 1982 (1-9
above) and summarizes the results. It also describes sample
collection, preservation, and transportation techniques. Finally
it describes the pollutant parameters quantified, the methods of
analyses, and the general approach used to ensure reliability of
the analytical data produced. The raw data obtained during these
programs are included in the record supporting the proposed rule
and are also discussed in Section VI, Wastewater
Characterization.
Detailed analytical data on conventional, nonconventional, and
toxic pollutant concentrations in raw and treated process
wastewater streams were collected in a comprehensive
sampling program. Data developed for the 1982 ore mining
regulations indicated that organic priority pollutants would not
be expected to be significant in placer mining wastewaters
because the paydirt (ore) consists of natural earth materials and
reagents are not generally used.
V-2
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Therefore/ the sampling efforts by the various groups listed
above were modified to emphasize certain pollutants.
The discussions that follow generally pertain to the most recent
sampling efforts undertaken by the EPA (1984, 1983, and 1982) and
its contractors, FTA (1983) and KRE (1984 and 1983), particularly
with respect to site selection and reconnaissance.
SITE SELECTION FOR RECONNAISSANCE STUDY
Faced with the responsibility for developing effluent
limitations for placer mining, EPA discovered that economic and
financial information about the Alaskan segment of the industry
was virtually non-existent. The largest body of such
information was the partial and anecdotal representations
developed in the course of public hearings. This lack of
information demonstrated the need to obtain data on mining
economics for use in formulating effluent limitations guidelines
and standards.
The Agency, with the cooperation of the miners, conducted an
information-gathering effort during the 1983 and 1984 mining
seasons. EPA had previously committed itself to an examination
of effluent and receiving water quality characteristics; this
two-year study was expanded to incorporate an economic and
financial component.
Site visits were conducted by EPA Region X personnel to seven
mines during the 1984 mining season. In addition, KRE conducted
V-3
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engineering site visits at ten mines (including several that were
covered by Region X) and visited an additional ten mines to
obtain economic and operational data during 1984. Frontier
Technical Associates (FTA) visited six placer gold mines in the
lower 48 states, five in Montana and one in California, to obtain
operational, economic and water quality information relative to
the operation of mines outside of Alaska.
Although EPA has historical data from gold placer mines from as
early as 1976 and many subsequent years, the Agency primarily
relied upon the studies performed in 1984 since these technical
data on treatment performance are relatively current and more
fully documented than early studies. The majority of the
available cost and economic data were also obtained in 1984. The
Alaska mine sites in the 1984 studies used both for engineering
site visits and sampling, were selected from available data from
previous studies and through discussions with EPA Region X,
Alaska Department of Environmental Conservation (ADEC), miners'
trade associations, the Placer Miners Advisory Committee (PMAC),
and individual miners. These mines were selected to be as
representative as possible of placer mines considering such
factors as: location, type of mining, size, amount and type of
overburden, topography, and treatment employed. The majority of
the data are for Alaska because the majority of placer mines in
the U.S. are located in Alaska. However, data on facilities in
the "lower 48" were also collected generally from state contacts
and some site visits. These data were also used in the analyses.
All site visits included the collection of data on existing
V-4
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treatment, and the Alaska work provided data on pilot-scale
treatment technology, high rate recycle, costs of operations and
treatment, and the economic viability of mines.
Actual engineering site visits (reconnaissance visits) were
conducted by EPA Region X personnel (49 sites), Frontier
Technical Associates (five sites), and Kohlmann, Ruggiero
Engineers (six sites) during the 1983 mining season. During
1982, EPA Region X also conducted reconnaissance sampling visits
at 51 sites. At each site sampled by FTA and KRE, two separate
sampling episodes were conducted (one mine had only one episode,
because it shut down soon after arrival of sampling personnel).
Although most of the sites visited by EPA had only one sampling
episode, a few were visited more than once.
Treatability studies consisting of on site settling tests were
conducted at a total of 19 different mines during the 1983 and
1984 mining seasons by Frontier Technical Associates and Kohlman,
Ruggiero Engineers. These settling tests included jar tests and
settling tube experiments employing unaided as well as
flocculant-aided settling.
For the 1983 sampling effort conducted by Region X
(Reconnaissance Study), a size-structured random sample was drawn
from 409 Tri-Agency Annual Placer Mining Applications on file at
EPA Region X. A primary sampling group of 34 mines was
supplemented by a similarly structured secondary group of 31
mines to provide an adequate sample in the event of nonresponse,
failure to locate, intermittent or ceased operations, or other
V-5
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obtacles to information-gathering and sampling.
The 34-mine sample proved impossible to achieve. Distance,
accessibility, intermittent nature of the industry, equipment
breakdowns, and locational uncertainties combined to reduce the
sample size. Both time and budget constraints made it necessary
to treat the primary and secondary sample components as a single
sample of 65 mines, and to attempt to contact each potential
respondent at least once rather than to make repeated visits to
the primary sample group in order to verify the operational
status of each. The characteristics of the sampling effort are
presented in Table V-l prepared by EPA Region X, while a list of
facilities visited (by mine code) for EPA, FTA, and KRE is
presented in Table V-2.
Effluent samples were obtained at each mine visited in 1983 and
1984 that was visited during the time the mine was sluicing. The
parameters that were analyzed by EPA, FTA and KRE during the
reconnaissance program are shown in Table V-3.
Samples at each mine were obtained from the following locations:
1. Intake water
2. Influent to treatment
3. Effluent from treatment
4. 500 feet downstream of discharge into receiving stream
Sample numbers, locations, dates, times, etc. were noted and a
sketch of the site and sample locations was prepared. Field
measurements of pH, temperature, turbidity, and settleable solids
were recorded.
V-6
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Table V-l. Composition of Sampled Mining Operations
(Respondents to EPA Region X Economic Survey; Source: EPA
Region X).
Category Number of Respondents
Small:
No Recyle 9
Partial Recycle 5
Full Recycle 7
Medium:
No Recycle 6
Partial Recycle 6
Full Recycle 7
Large:
No Recycle 1
Partial Recycle 1
Full Recycle 1
Total Sample: 65
Positive Response: 43
Non-Response: 1
Status Undetermined: 21
*Sluicing capacity:
Small: 100-750 cu.yd./day
Medium: 750-3500 cu.yd./day
Large: >3500 cu.yd./day
V6a
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Table V-2. List of Facilities Visited in the Reconnaissance
Sampling Effort.
MINE CODE
EPA83 EPA82 FTA8 3 KRE83 FTA84 KRE84 EPA84
4107 X
4109 XX X
4110 X X
4126 X
4127 X
4132 X
4133 X
4134 X X
4138 X
4167 X
4168 X
4169 XX X
4170 X X
4171 X X
4172 X X
4173 XX X X
4174 X X
4175 X X
4176 X X
4177 X
4178 X
4179 X
4180 XX X
4181 X
4182 X
4184 X
4185 XX X
4186 X
4187 X
4188 X
4189 XX X
4190 X X
4191 X
4192 X
4193 X X
4194 X
4195 X
4196 X
4197 X X
4198 X
4199 X
V-6b
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Table V-2. (Cont.)
MINE CODE
..EPA83 EPA82 FTA83 KRE83 FTAR4
4200
4201
4202
4203
4204
4205
4206
4207
4208
4209
4210
4211
4212
4213
4216
4217
4219
4222
4223
4224
4225
4226
4227
4229
4230
4231
4232
4233
4Z34
4235
4236
4237
4239
4240
4241
4242
4243
4244
4245
4247
4248
4249
4250
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
KRRS4 RPAfi/t
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
V- 6
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Table V-2. (Cont.)
MINE CODE
EPA83 EPA82 FTA83 KRE83 FTA84 KRE84 EPA 8A
4251 x
4252 X
4253 x
4254 X
4255 X
4260 x
4262 x
V- 6d
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Table V-3. List of sample parameters by Study Group.
Parameter
pH
TSS
Set. Solids
Turbidity
Total As
Diss. As
Tot . Rec . As
Tot. Hg
Diss. Hg
Spec. Gravity
Temperature
EPA (1983)
X
X
X
X
X
X
X
**
**
X
X
FTA (
X
X
X
X
X
X
X
X
X
-
X
X X
X X
X X
X X
X X
X
X
X X
** Only a few sites sampled by EPA were analyzed for mercury.
V6
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At each site visited by Region X, KRE, and FTA, technical
operating data as well as financial data were collected during an
interview using a fact sheet. Each miner was requested to discuss
the operational economics and financing of his mine. The
interviews followed an outline prepared by EPA Region X (1983)
and EPA/ITD (1984). The miners were informed of the purpose and
voluntary nature of the interview, and were assured code numbers
independent of other means of identification would be up for the
sample group and are used in this report.
Employment of a pre-selected random sample as an information
gathering procedure was used by Region X in the 1983 study based
largely upon the needs of the economic component of the study.
The Agency had sampled effluent and receiving waters during the
1982 mining season, employing the simple selection strategy of
taking samples at any mine whose sluice was in operation at the
time it was visited. It was reasoned that information developed
only from mines with operational sluices might bias the economic
study toward the more efficient and better situated operations.
Stratification of the sample was based on the requirements of the
water sampling portion of the study. This was intended to obtain
information from mines of various sizes and with a broad range of
sluice water treatment or controls (e.g., sedimen-tation,
recycle). The final composition of the sample was a compromise
that reflected the competing requirements of economic and
effluent control data-gathering. The table below presents a
V-7
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summary comparison of the size distribution of permitted mines in
Alaska and the mines sampled:
Permitted Sampled
Size* Mines Mines**
100-750 cu.yd./day 78% 49%
750-3500 cu.yd./day 20% 44%
>3500 cu.yd./day 3% 7%
Mean Capacity (yd3/day) 756 1170
Mean Employment (persons) 4.3 6.0
* Sluicing capacity
** Applies to EPA 1983 Region X sampling only (PTA and KRE
sampled two mines not sampled by EPA)
V-8
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SAMPLE COLLECTION, PRESERVATION, AND TRANSPORTATION
Collection, preservation, and transportation of samples were
accomplished in accordance with procedures outlined in Appendix
III of "Sampling and Analysis Procedures for Screening of
Industrial Effluents for Priority Pollutants" (published by the
EPA Environmental Monitoring and Support Laboratory, Cincinnati,
Ohio, March 1977, revised April 1977) and in "Sampling Screening
Procedure for the Measurement of Priority Pollutants" (published
by the EPA Effluent Guidelines Division, Washington, D.C.,
October 1976). Analysis of conventional and nonconventional
pollutants were performed according to the following EPA methods:
Parameter EPA Method
pH 150.1
TSS 160.2
Sett. Solids 160.5
Temperature 170.1
Turbidity 180.1
All methods listed above are from "Methods for Chemical Analysis
of Water and Wastes," EPA Report No. EPA/4-79-020, March 1979,
USEPA Enviromental Monitoring and Support Laboratory, Cincinnati,
OH.
All samples obtained were grab samples. In general, the following
types of samples were collected at each site:
1. Total suspended solids—sample filtered in the field using
preweighed glass fiber filters; filter weighed subsequently
in the laboratory;
2. Total metals—sample collected for determination of total
arsenic and mercury; preserved in the field with 1:1 HNO3
V-9
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to a pH less than 2;
3. Total recoverable metals—samples collected for determination
of total recoverable arsenic; preserved in the field with
five ml/1 concentrated nitric acid;
4. Dissolved metals—sample filtered through a 0.45 micron
filter; preserved with 1:1 HNO3 to a pH less than 2;
5. Settleable solids—determined immediately in the field using
an Imhoff cone;
6. Turbidity—sample analyzed in the field using a field
nephelometer (dilutions often necessary);
7. pH and Temperature—analyzed in the field using a calibrated
pH meter and a thermometer.
All sample containers were labeled to indicate sample number,
sample site, sampling point, individual collecting the sample,
type of sample (influent, effluent, etc.), sampling dates and
times, preservative used (if any), etc.
All samples being sent for outside analysis were packed in
waterproof plastic foam-insulated chests which were used as
shipping containers. Sample shipments were made by air freight
to the laboratories as soon as possible.
Associated Data Collection
Drawings and other data relating to mine operations were obtained
during site sampling visits. These additional data included
information on production, sluice capacity, operating days,
number of employees, mining methods, ore grade, water use and
source, wastewater treatment and control, etc. Sketches of each
site were prepared showing sample locations, site layout, etc. A
trip report was prepared for each site giving the results of the
data collection effort as well as sampling results.
V-10
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SECTION VI
WASTEWATER CHARACTERIZATION
The sampling programs described in Section V provided the data
EPA used to determine the presence and concentration of
pollutants in placer mining wastewater. These data, "wastewater
characterization," are available in the public record along with
details of their collection, screening and evaluation. In
developing effluent limitations and standards, EPA relied
primarily on the 1984 reconnaissance and the 1984 treatability
data. EPA found that earlier data collection efforts did not
always document the operating conditions of the treatment system
at the mine sites. However, the 1984 data (Group I) does take
into account the maintenance, construction and operation of
treatment systems that are typical of mines found in Alaska.
For the purpose of the wastewater characterization, the
reconnaissance data have been classified into three groups:
Group
I. 1984 data collected by Kohlmann Ruggiero Engineers (KRE).
II. 1984 data collected by KRE plus the 1984 data collected in
long-term sampling by Region X.
III. 1983 data collected by Frontier Technical Associates (FTA)
and KRE together with the 1984 data from Group II above.
Data that passed the Agency's engineering evaluation of the
treatment ponds, as discussed below, are included in the three
groups. The data in Group I are contained in Group II, and the
Vl-1
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data in Group II are contained in the data in Group III. All
three groups were analyzed. It was not possible, however, to
subject the Group II and Group III data to a rigorous engineering
evaluation because some essential information concerning the
settling pond systems was not well documented during the site
visits conducted in 1983. Missing information includes pond
area, pond depth, pond short-circuiting, "scouring" from the
ponds, quiescent settling or turbulent flow conditions. The
evaluation of the data in Group I includes the information
obtained at the time the mines were selected and at the time the
existing treatment was sampled. Existing treatment was evaluated
by sampling influent, and raw and treated effluent; observing
flow patterns in the ponds to identify short-circuiting;
determining retention times in the ponds; and determining flows
to and from the mines.
The wastewater samples were analyzed for settleable solids, total
suspended solids, turbidity, and in some cases, total arsenic,
and total mercury. Appendix VI-2 contains a complete listing of
the data that was used by the Agency in each of the three groups.
The Agency developed long term averages for settleable solids
(SS), total suspended solids (TSS), and turbidity (NTU) based on
each of the three groups of data described. In developing these
levels, EPA assumed that the data followed a delta-lognormal
distribution as explained in Appendix VI-1. (See Aitchison and
Brown, The Lognormal Distribution.) The use of the delta-
lognormal distribution is based on past experience with data on
pollutant levels. When there are no values below the detection
VI-2
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limit, the delta-lognormal distribution is the usual lognormal
distribution. The Agency used Group I data to develop effluent
limitations for daily and long term levels. For comparison, EPA
calculated limitations based on the data from each of the three
groups. The daily levels apply to a single grab sample taken in
the effluent from a mine because the delta-lognormal distribution
was applied to data on the individual grab samples.
The results of the calculations are given in Table VI-1 for the 3
data groups. In developing confidence levels of treatment
effectiveness, EPA used the delta-lognormal distribution as
explained in Appendix VI-1.
In using the delta-lognormal, the Agency used estimates of the
proportion below the detection limit, and the log-variance,
, that was pooled over mines. Individual estimates by mine
were used for the log-means, The statistical expressions used
to compute the daily and monthly levels are listed in Appendix
VI-1. A summary of daily and monthly levels is in Table VI-1.
Treatablility Analysis
The 1984 field work of installed treatment performance
also included some pilot scale treatability studies (discussed in
Section VIII) which compared unaided settling with settling
assisted by various poly-electrolytes (flocculants). For
wastewater samples from operating mines, these studies seem to
show the potential improvement in treatment that could be
achieved by using poly-electrolytes to assist simple, unaided
VI-3
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settling at full scale. For each site/ samples of raw discharge
were prepared as described in the "1984 Alaskan Placer Mining
Study and Testing Report," Kohlmann Ruggiero Engineers, January
31, 1985. This report also contains all the detailed results of
the settling tests for each of the polyelectrolytes tested.
TABLE VI-1
Daily and Long Term Levels for Settleable Solids (SS),
Total Suspended Solis (TSS), Turbidity (NTU)
Settleable
Data Solids
Used ml/1
Group
I K
II K
III K,
Daily
1984 1.1
& R-10 1984 0.9
F, R-10 83/84 3.2
Monthly
0.2
0.2
0.5
TSS
mg/1
Daily
11,600
6,800
6,300
Monthly
2,400
1,800
1,700
Turbidity
NTU
Daily
7,900
4,400
3,400
Monthl
2,600
1,800
1,400
Index
Data
K - Kohlmann Engineering Data - 1984
R-10 - Region 10 Data - 1984
F - Frontier Data - 1983
Method based on the delta-lognormal distribution (see Appendix
VI-1).
NOTE: Settleable solids detection limits used = 0.1 ML/L.
Because of the ability to control sampling and settling
conditions, pilot test data are used here to:
1. Establish the correlations of total suspended solids with
VI-4
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arsenic and mercury.
2. Verify long-term averages for settleable solids and total
suspended solids with unaided settling and verify preliminary
engineering judgement that flocculant-assisted settling was
possible; define general operating parameters, and proper dose
rates.
Correlations of_ Total Suspended Solids (TSS) with Arsenic (As)
and Mercury (Hg)
The correlations of total suspended solids with arsenic and
mercury as shown in Appendix VI-3B and Appendix VI-3C, support
the general expectation that arsenic and mercury are components
of the total suspended solids. Consequently, treatment or
control of total suspended solids in the effluent will provide a
corresponding control of these correlated pollutants. The
correlations of TSS with arsenic and mercury are important
because there were too few determinations of effluent arsenic and
mercury to reliably establish the effectiveness of treatment for
these pollutants. The treatability data used for the
correlations are given in Appendix VI-3 along with a graphical
display of the data. The Spearman rank correlations are 0.83 for
TSS with As and 0.61 for TSS with Hg. These correlations are
statistically significant (P <_ 0.05). The Spearman rank
correlation was used because this correlation is not affected by
transformations that do not change the order of the pollutant
measures. For example, log-transformed values would have the
same Spearman rank correlations.
VI-5
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Long-Term Averages for Treatability Data
The two-hour settling test data summarized in Appendix VI-4 was
used to compare simple settling with the flocculant assisted
settling. The long-term averages for these tests are shown in
Table VI-2. These comparisons are based on the two-hour data
from all mines in the settling study. These pilot study results
show the flocculant-assisted settling provides a substantial
reduction in SS and TSS over simple settling.
These data were also used as a basis for comparison with test
results at actual mines of the long-term averages for TSS and SS
with pilot test settling at 2, 3 and 6 hours. Pilot test results
and actual performance of ponds were both defined from effluent
samples taken from mines used in the evaluation of existing
treatment. To evaluate the suitability of existing treatment, a
preliminary visit was conducted at a group of mines. Sites were
then chosen for long term sampling of existing treatment and
pilot testing. Subsequently, it should be noted that upon
arrival for sampling and testing, several of the selected mines
were found to have undergone substantial degradation in treatment
during the interim or to be otherwise inappropriate choices to
represent a minimum standard of treatment. These facilities were
omitted from the analysis of existing treatment and, for
consistency, from the analysis of treatability data. In
particular, one mine had completely filled its settling pond with
solids, one mine was suffering from scouring of solids from the
ponds, one mine was recycling 100 percent of its wastewater, and
VI-6
-------
one mine was encountering overburden with a very high percentage
of colloidal material.
A summary of long-term averages from the treatability tests is
given in Table VI-3. Table VI-3 shows that between 3 and 6 hours
settling time can achieve concentrations of settleable solids
below 0.2 ml/1.
VI-7
-------
TABLE VI-2
Table of the Long-Term Average for Settleable Solids (SS) and
Total Suspended Solids (TSS) with
Two-Hours of Plain Settling and Two-Hours of Flocculant Assisted
Settling
Data Used* Settleable Solids Total Suspended Solids
KRE-1984 SS ml/1 TSS mg/1
Without flocculant 1.1 7,090
With flocculant ** 26
*See Appendix VI-4
**Eight values all at or below the SS detection limit of 0.1
ml/1.
VI-8
-------
TABLE VI-3
Table of Long-Term Averages for
Settleable Solids (SS) and Total Suspended Solids (TSS)
With Plain Settling at Two Hours, Three Hours, and Six Hours
Data Used* Settleable Solids Total Suspended Solids
KRE-1984 SS ml/1 TSS rag/1
Plain Settling
2 hours 0.8 5040
3 hours 0.2 4300
6 hours ** 3450
*Kohlmann Engineering Test Data with Mines 4169, 4247, 4248, and
4251 deleted.
**Five observations at or below the SS detection limit of 0.1
ml/1.
VI-9
-------
Virtually all commercial gold placer mines operating in 1984 and
1985 had settling ponds of varying numbers, sizes, and
efficiencies. However, most of the ponds observed by EPA and the
EPA contractors, and the data that has been obtained on existing
ponds indicates that the ponds lack in design, construction, or
maintenance to consistanfcly produce an acceptable effluent
quality or concentration of solids (settleable solids and TSS).
TSS effluent limitations for eleven other subcategories of the
ore industry were promulgated and the limitations sustained in
the courts with a daily maximum of 30 mg/1 based on treatment
facilities being constructed and maintained to provide 24 hours
retention. A retention time of 24 hours at most placer mines is
not practicable as discussed in Section X. In Section VIII and
IX of this document, treatment facilities to control solids with
simple setttling technology are designed and costed to provide 6
hours of settling in well designed, constructed, and operated
settling ponds which reduce the flow velocity to a minimum and
have sufficient volume for sludge to preclude remixing or cutting
of solids from the sludge back into the effluent. Though the
long term levels for solids based on 1984 data from existing
treatment at placer mines is 0.2 ml/1 settleable solids, the
calculated daily maximum is over 0.2 ml/1. However, the data
used to calculate these levels include some data points or grab
samples, which are believed to represent poor sampling
techniques, upsets of the treatment, an overload or slug to the
treatment, short circuiting, or poor maintenance. These data
points are "out liers" because they generally exceed the
VI-10
-------
variability found in well constructed and maintained ponds.
The instantaneous maximum settleable solids limitation being
proposed is 0.2 ml/1 based on simple settling in properly
designed, constructed and operated ponds providing 6 hours of
retention time. Long term average (monthly average) TSS
limitation being proposed is 2000 mg/1 based on simple settling.
VI-11
-------
APPENDIX VI-1
STATISTICAL METHODOLOGY
VI-1-1
-------
$%Methodology and Algorithm for Developing$%
$%Daily and Monthly Achievable Levels$%
The methodology used for calculation of achievable levels or
limits is described below. For these calculations, the data are
assumed to follow the delta-lognormal distribution (J. Aitchison
and J.A.C. Brown (1957). $%The Lognormal Distribution$%,
Cambridge University Press) in which 6 is the proportion of
observations, if any, at or below the detection limit. For the
reconnaissance data, the parameter y takes on distinct values
for each mine, while the parameters 6 and o2, and y , were
taken as common because there were too few data values to obtain
separate parameter estimates for each mine. Consequently, to
apply the following formulae to the treatability data, use the
formulae as if there were only one mine.
Consider the data for a pollutant such as settleable solids
•Let Xij represent jtn observation for itn mine where
there are a total of c mines.
Hence for XJLJ, i - 1, ..., c
J ~ 1, «.., nj^
where n, = number of observations for mine i
VI-1-2
-------
and
c
N = I r»i = total number of observations.
Let DL = detection limit. Hence, for each mine we calculate
n» = the number of obsrvations for mine i DL.
c
Let M • £ m * total number of observations overall DL
Hence,
(ni - mj.) » number of observations for mine i > DL
and
c
2 (ni - mi) "'N-M* total number of observations
i*l overall > DL
VI-1-3
-------
1. Let 6 = M/N represent the overall proportion of observations
less than or equal to the detection limit.
2. The mean of the logtransformed values, excluding
observations at or below the detection limit is calculated
for each mine via:
v A * X
A - 2 yij/(ni - mi)
where yij = In(xij) i = 1, ..., c
3 ~ 1, •••, ni
3. The variance of the logtransformed values, excluding
observations at or below the detection limit, is calculated
via:
£ £ (y i j - y~i. ) 2
o2 = c
I (ni-mi-1)
_
where yi. = j Yij/(ni - mi)
J-l
VI-1-4
-------
4. Mean of delta-lognormal distributions for each mine is:
Ei - 6 (DL/2) -»- (1 - fi )lexp(pi + o2/2)l
where DL is the detection limit.
The long-term averages for the treatability studies shown in
Tables VI-2 and VI-3 are computed using this expression for the
mean of the delta-lognormal distribution. In the treatability
studies the settling data were analyzed without distinguishing
the mines because of the limited data available.
5. Variance of delta-lognormal distributions for each mine is:
/s
2 yi + o2 o2
= (1 - 6 )[e ] [e - (1 - 6)1
6. Daily achievable-level calculated for each mine is:
yi + 2(0.99) a
LI = e
VI-1-5
-------
(p \
0.99 - °_\
*• /
1 - 6/
7. Monthly achievable-level calculated for each mine is:
L30i = Ei + Z(0.95) * Vi(30)
where Vi(30) • /Vi/30.
8. Overall daily achievable-level is:
c
MU1 - l Li/C,
This level limits the value of a single grab sample
9. Overall monthly achievable-level is:
c
MU30 = i L30j./c.
The monthly achievable-level is based on 30 grab samples
during the month.
Note imputations used:
A
a. If there does not exist a y^ for any particular mine, then
A A
set Pi » overall y
A c ni~mi
where y • I I yii/(N - M).
ill j:l
b. if no values exist below the detection limit, then the above
formulae reduce to the assumption that the concentration
values follow a lognormal distribution.
VI-1-6
-------
APPENDIX VI-2
LISTING OF EFFLUENT POLLUTANT VALUES FOR
SETTLEABLE SOLIDS (SS),
TOTAL SUSPENDED SOLIDS (TSS),
TURBIDITY,
ARSENIC
AND
MERCURY
BY MINE NUMBER
(GROUP III DATA GROUPS I AND II ARE SUBSETS OF GROUP III)
VI-2-1
-------
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APPENDIX VI-3
A. Treatability Data Used to Establish the
Correlations of TSS with AS and Hg.
B. Graphical Presentation of the Data in A.
C. Sinrary of the TSS Correlations with
As and Hg.
VI-3-1
-------
APPENDIX VI-3A
Treatability Data Used to Establish the Correlations of
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VI-3-3
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APPENDIX VI-3B
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VI-3-6
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APPENDIX VZ-3C
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APPENDIX VI-4
Summary of 1984 Treatability Data Used to
Compare Plain Settling with
the Best Flocculant Settling at
Two-Hour*; Using All Minns
VI-4-1
-------
A VI-4
During 1984, treatability experiments were performed by KRE for the
USEPA-ITD. Settling tests were run both with and without flocculant addition.
These experiments are nore completely described in Section VIII of .this
document. Table VI-^ sunmarizes the results of two-hour samples taken during
these tests at each of the ten mines studied.
VI-4-2
-------
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VI-4-3
-------
SECTION VII
SELECTION OF POLLUTANT PARAMETERS
The Agency has studied placer mining wastewaters as well as other
ore mining and dressing wastewaters to determine the presence or
absence of toxic, conventional, and nonconventional pollutants.
According to the requirements of the Clean Water Act of 1977
(CWA), 129 toxic or "priority" pollutants are to be studied in
the formulation of these guidelines (see Section 307 (a)(l),
Table 1 of the Act).
EPA and its contractors conducted sampling and analysis at
facilities which represented a wide range of locations,
operating conditions, processes, water use rates, topography,
production rates, and treatment technologies (settling ponds-
single or multiple; recycle-partial and total). Any of the
priority pollutants present in treated effluent discharges are
subject to regulation by BAT effluent limitations guidelines.
The Settlement Agreement in Natural Resources Defense Council v_._
Train, 8 ERC 2120 (D.D.C. 1976), modified 12 ERC 1833 (D.D.C.
1979) and by October 26, 1982, August 2, 1983, January 6, 1984,
July 5, 1984, and January 7, 1985 provides a number of provisions
for the exclusion of particular pollutants and categories of
pollutants from regulation. Although this regulation is not
being issued under a schedule established in the NRDC Consent
Decree, EPA has decided to apply the criteria for regulating (or
in the alternative excluding from regulation) toxic pollutants of
VII-1
-------
classes of pollutants established in Paragraph 8 of the
Agreement.
The criteria for exclusion of pollutants are summarized below:
1. Equal or more stringent protection is already provided by an
effluent limitation guideline or standard promulgated pursuant to
Section 301, 304, 306, 307(a), or 307(c) of the CWA.
2. The pollutant is present in the effluent discharge solely as
the result of its presence in the intake water taken from
the same body of water into which it is discharged.
3. The pollutant is not detectable in the effluent within the
category by approved analytical methods or methods
representing the state-of-the-art capabilities.
4. The pollutant is detected in only a small number of sources
within the category and is uniquely related to only those
sources.
5. The pollutant is present in only trace amounts and is
neither causing nor likely to cause toxic effects.
6. The pollutant is present in amounts too small to be
effectively reduced by technologies known to the
Administrator.
7. The pollutant is effectively controlled by the technologies
upon which are based other effluent limitations and
guidelines.
DATA BASE
The table on the next page presents a summary of the data sources
consulted for various aspects of this study:
Reference Ref. No.
1. BPT Development Document and Supplements for Ore (1)
Mining
2. BAT Development Document and Supplements for Ore (2)
VII-2
-------
Mining
Reference Ref. No.
3. FTA Treatability Study-1983 (3)
4. KRE Treatability Study-1983 (4)
5. EPA Reconnaissance Study-1983
6. FTA Reconnaissance Study-1983 (3)
7. EPA Reconnaissance Study-1982
8. R&M Consultants-1982 (5)
9. Environment Canada—1983 Yukon Study (6)
10. Canadian Dept. of Indian & North. Affairs (7)
11. Calspan Reconnaissance Study-1979 (8)
12. EPA-NEIC 1977 Reconnaissance Study (9)
13. Alaska DEC Reports (10)
14. Dames & Moore-1976 Reconnaissance Study (11)
15. KRE Reconnaissance Study - 1984 (12)
16. EPA Region X Reconnaissance/Treatability
Study - 1984
17. Shannon and Wilson Study - 1984 (13)
These sources of data describe numerous studies performed by the
EPA and Alaska Department of Environmental Conservation (ADEC)
VII-3
-------
and their contractors for each. Extensive data have been
developed during the course of these studies, and these data have
been used to choose the pollutant parameters for regulation as
well as those excluded from regulation.
SELECTED POLLUTANT PARAMETERS
Several conventional and nonconventional pollutants were found in
the wastewater of each of the facilities visited. Most of the
sampling efforts for toxic pollutants associated with the placer
mining industry located in Alaska have evaluated the arsenic and
mercury levels in the treated wastewater. Few studies have
evaluated the wastewater for the presence of other metals, or
other toxic pollutants. On the basis of its study of the entire
ore mining and dressing industry in the United States, EPA
excluded 114 of the toxic organic pollutants during the 1982 BAT
rulemaking for the industry (2). No information has been
developed during the course of these studies or provided to EPA
by the public which indicates that any of the organic priority
pollutants are present in amounts which are treatable. In
addition, organic reagents are not used in this industry because
it relies on gravity separation methods to extract gold from the
ore. Therefore, organic pollutants are not expected to be
present in the wastewater from placer mining operations.
The parameters considered for regulation in this industry
include:
Conventional: pH, Total Suspended Solids (TSS)
VII-4
-------
Nonconventional: Settleable Solids (SS), Turbidity
(TUR)
Toxics: Arsenic (AS) (total), Mercury (HG)
(total)
EXCLUSION OF TOXIC POLLUTANTS THROUGHOUT THE ENTIRE
SUBCATEGORY
Toxic Organic Compounds
The toxic organic compounds are primarily synthetic and generally
are not naturally associated with metal ores as mentioned above.
During the 1984 Reconnaissance Study by KREr samples for the
priority toxic organics were obtained and analyzed. Treated
final effluent samples from the following ten mines were analyzed
for the presence of toxic organics:
Mine 4169
Mine 4248
Mine 4249
Mine 4180
Mine 4173
Mine 4244
Mine 4250
Mine 4251
Mine 4247
Mine 4252
Only two priority organics were detected in the final effluent at
some of the mines. None of the remaining priority organics were
detected at any of the mines. The following priority organics
were detected:
Mine Pollutant Concentration
Mine 4249 Methylene Chloride 22 ug/1
VII-5
-------
Mine 4173 Methylene Chloride 23 ug/1
Mine 4247 Methylene Chloride 17 ug/1
Bis (2-Ethylhexyl)
Phthalate 68 ug/1
In the sampling for the priority organics, 117 toxic organics
were not detected and therefore were excluded from further
consideration based on Criterion 3 above (i.e., the pollutant is
not detectable by approved analytical methods). The two priority
organics detected are also being excluded based on Criteria 5
and 6 (i.e., the pollutant is present in only trace amounts and
is neither causing nor likely to cause toxic effects; and the
pollutant is present in amounts too small to be effectively
reduced by technologies known to the Administrator). In
addition, the presence of these two priority organics in other
mining industries has been attributed to sample and laboratory
contamination (2); EPA believes such contamination is the source
of these pollutants in placer mine wastewater as well.
Current placer gold mining practice does not use reagents or
chemicals for the processing of gold from paydirt. All
processing relies on physical or gravity separation, so any
contaminants or pollutants present generally would originate from
the ore itself naturally. In addition, oil and grease could be
present in some instances from hydraulic fluids or fuels.
Ordinarily, good housekeeping practices will control this
parameter. Therefore, based on data available for the ore mining
industry as a whole and knowledge of the processes and ores
exploited for placer gold mining, the Agency proposes to exclude
VII-6
-------
all toxic priority organic pollutants.
Toxic Metal Pollutants
Table VII-1 presents the results of toxic metals sampling at ten
Alaskan placer mines during 1984, which was performed for USEPA
by one of its subcontractors, Kohlmann Ruggiero Engineers. These
toxic metal pollutants are excluded from regulation based on
Criteria 3, 5 and 6 (see selection of pollutant parameters). The
remaining toxic metals, arsenic and mercury, are excluded based
on Criterion 7 (the pollutant is effectively controlled (or
removed) by the technologies upon which are based other effluent
limitations and guidelines). See Section VI.
CONVENTIONAL POLLUTANT PARAMETERS
This parameter is regulated for every segment of the ore mining
and dressing point source category. High or low pH values can
result in solubilization of certain ore components and can
adversely affect receiving water pH. Acid conditions can result
in the oxidation of sulfide minerals in certain ores. To the
best of the Agency's knowledge and belief, based upon the
extensive sampling to date, pH problems have not been encountered
in placer mining discharges.
Total Suspended Solids (TSS) and Turbidity (TUR)
Suspended solids and turbidity are important parameters in both
municipal and industrial water supply practices. Finished
VII-7
-------
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drinking waters have a maximum limit of 1 turbidity nit where the
water enters the distribution system. This limit is based on
health considerations as it relates to effective chlorine
disinfection. Suspended matter provides areas where
microorganisms do not come into contact with the chlorine
disinfectant (NAS, 1974). The ability of common water treatment
processes (i.e., coagulation, sedimentation, filtration, and
chlorination) to remove suspended matter and achieve acceptable
final turbidities is a function of the composition of the
material as well as its concentration. Because of the variablity
of such removal efficiency, it is not possible to delineate a
general raw water criterion for these uses.
Turbid water interferes with recreational use and aesthetic
enjoyment of water. Turbid waters can be dangerous for swimming,
especially if diving facilities are provided, because of the
possibility of unseen submerged hazards and the difficulty in
locating swimmers in danger of drowning (NAS, 1974). The less
turbid the water the more desirable it becomes for swimming and
other water contact sports. Other recreational pursuits such as
boating and fishing will be adequately protected by suspended
solids criteria developed for protection of fish and other
aquatic life.
Fish and other aquatic life requirements concerning suspended
solids can be divided into those whose effect occurs in the water
column and those whose effect occurs following sedimentation to
the bottom of the water body. Noted effects are similar for both
fresh and marine waters.
VII-8
-------
The effects of suspended solids on fish have been reviewed by the
European Inland Fisheries Advisory Conunmission (1965). This
review identified four means by which suspended solids adversely
affect fish and fish food populations:
(1) by acting directly on the fish swimming in water which
solids are suspended, and either killing them or re-
ducing their growth rate, resistance to disease,
etc etera;
(2) by preventing the successful development of fish
eggs and larvae;
(3) by modifying natural movements and migrations of fish;
(4) by reducing the abundance of food available to the
fish.
Settleable materials which blanket the bottom of water bodies
damage the invertebrate populations, block gravel spawning beds,
and if organic, remove dissolved oxygen from overlying waters
(EIPAC, 1965; Edberg and Hofsten, 1973). In a study downstream
from the discharge of a rock quarry where inert suspended solids
were increased to 80 mg/1, the density of macroinvertebrates
decreased by 60 percent while in areas of sediment accumulation
benthic invertebrate populations also decreased by 60 percent
regardless of the suspended solid concentrations (Gammon, 1970).
Similar effects have been reported downstream from an area which
was intensively logged. Major increases in stream suspended
solids (25 ppm suspended solids upstream vs. 390 ppm downstream)
caused smothering of bottom invertebrates, reducing organism
density to only 7.3 per square foot versus 25.5 per square foot
VII-9
-------
upstream (Tebo, 1955).
Solids in suspension that will settle in one hour under quiescent
conditions because of gravity are settleable solids.
When settleable solids block gravel spawning beds which contain
eggs, high mortalities result although there is evidence that
some species of salmonids will not spawn in such area (EIFAC,
1965).
It has been postulated that silt attached to the eggs prevents
sufficient exchange of oxygen and carbon dioxide between the egg
and the overlying water. The important variables are particle
size, stream velocity, and degree of turbulence (EIFAC, 1965).
Deposition of organic materials to the bottom sediments can cause
imbalances in stream biota by increasing bottom animal density,
principally worm populations, and diversity is reduced as
pollution-sensitive forms disappear (Mackenthun, 1973). Algae
likewise flourish in such nutrient-rich areas although forms may
become less desirable (Tarzwell and Gaufin, 1953).
Plankton and inorganic suspended materials reduce light
penetration into the water body, reducing the depth of the photic
zone. This reduces primary production and decreases fish food.
The NAS committee recommended that the depth of light
penetration not be reduced by more than 10 percent (NASf 1974).
Additionally, the near surface waters are heated because of the
greater heat absorbency of the particulate material which tends
to stabilize the water column and prevents vertical mixing (NAS,
VII-10
-------
1974). Such mixing reductions decrease the dispersion of
dissolved oxygen and nutrients to lower portions of the water
body. Accordingly, the Agency proposes to regulate settleable
solids, total suspended solids, and turbidity.
Arsenic
Arsenic is found to a small extent in nature in the elemental
form. It occurs mostly in the for of arsenites of metals or as
arsenopyrite (FeS2.FeAs2).
Arsenic is normally present in sea water at concentrations of 2
to 3 micrograms per liter and tends to be accumulated by oysters
and other shellfish. Concentrations of 100 mg/kg have been
reported in certain shellfish. Arsenic is a cumulative poison
with long-term chronic effects on both aquatic organisms and
mammalian species, and a succession of small doses may add up to
a final lethal dose. It is moderately toxic to plants and highly
toxic to animals—especially, as arsine (AsH3).
Arsenic trioxide, is exceedingly toxic, when it was studied in
concentrations of 1.96 to 40 mg/1, it was found to be harmful in
that range to fish and other aquatic life. Work by the
Washington Department of Fisheries on pink salmon has shown that
a level of 5.3 mg/1 of As2O3 for 8 days is extremely harmful to
this species; on mussels, a level of 16 mg/1 is lethal in 3 to 16
days.
Severe human poisoning can result from 100-mg concentrations, and
130 mg has proved fatal. Arsenic can accumulate in the body
VII-11
-------
faster than it is excreted and can build to toxic levels from
small amounts taken periodically through lung and intestinal
walls from the air, water, and food. Arsenic is a normal
constituent of most soils, with concentrations ranging up to 500
mg/kg. Although very low concentrations of arsenates may
actually stimulate plant growth,, the presence of excessive
soluble arsenic in irrigation waters will reduce the yield of
crops, the main effect appearing to be the destruction of
chlorophyll in the foliage. Plants grown in water containing one
mg/1 of arsenic trioxides show a blackening of the vascular
bundles in the leaves. Beans and cucumbers are very sensitive,
while turnips, cereals, and grasses are relatively resistant. Old
orchard soils in Washington that contain 4 to 12 mg/kg of arsenic
trioxide in the topsoil were found to have become unproductive.
Arsenic is known to be present in many complex metal ores—
particularly, the sulfide ores of cobalt, nickel and other
ferroalloy ores/ antimony, lead, gold and silver. It may also be
solubilized in mining and milling by oxidation of the ore and
appear in the effluent stream.
Mercury
Elemental mercury occurs as a free metal in certain parts of the
world; however, since it is rather inert and insoluble in water,
it is not likely to be found in natural waters. Although
elemental mercury is insoluble in water, many of the mercuric and
mercurous salts, as well as certain organic mercury compounds,
are highly soluble in water. Concentrations of mercury in
VII-12
-------
surface waters have usually been found to be much less than 5
micrograms per liter.
The accumulation and retention of mercurial compounds in the
nervous system, their effect on developing tissue, and the ease
of their transmittal across the placenta make them particularly
dangerous to humans. Continuous intake of methyl mercury at
dosages approaching 0.3 mg Hg per 70 kg (154 Ib) of body weight
per day will, in time, produce toxic symptoms.
Mercury's cumulative nature also makes it extremely dangerous to
aquatic organisms, since they have the ability to absorb
significant quantities of mercury directly from the water as well
as through the food chain. Methyl mercury is the major toxic
form; however, the ability of certain microbes to synthesize
methyl mercury from the inorganic forms renders all mercury in
waterways potentially dangerous. Fresh-water phytoplankton,
macrophytes, and fish are capable of biologically magnifying
mercury concentrations from water 1,000 times. A concentraction
factor of 5,000 from water to pike has been reported, and factors
of 10,000 or more have been reported from water to brook trout.
The chronic effects of mercury on aquatic organisms are not well-
known. The lowest reported levels which have resulted in the
death of fish are 0.2 micrograms per liter of mercury, which
killed fathead minnows exposed for six weeks. Levels of 0.1
microgram per liter decrease photosynthesis and growth of marine
algae and some freshwater phytoplankton.
SURROGATE/1NDICATOR RELATIONSHIPS
VII-13
-------
The Agency believes that it may not always be feasible to
directly limit each toxic which is present in a waste stream.
Surrogate or indicator relationships provide an alternative to
direct limitation of toxic pollutants accoring to Criterion 7.
Section VI discusses the data analysis which has been performed
to determine the presence of total arsenic and mercury in placer
gold mining treated effluent. Based upon the relationships
developed/ these metals have been shown to be associated with the
suspended portion of the wastewater stream rather than the
dissolved. Furthermore, the data available to the Agency
indicate that control of TSS will result in control of the toxic
metals to levels below those normally considered to be possible
with chemical treatment technologies as used in other segments of
the ore mining industry. The levels achieved both in the
reconnaissance sampling and treatability studies indicate that
control of TSS to the levels indicated will result in arsenic and
mercury levels near or below the Alaska water quality criteria
levels most of the time (see Section VI).
VII-14
-------
SECTION VII
REFERENCES
1. USEPA, "Develoment Document for Interim Final and Proposed
Effluent Limitations Guidelines for the Ore Mining and
Industry," EPA Report No. EPA 440/1-75/061C, October, 1975.
2. USEPA, "Development Document for Effluent Limitations
Guidelines and Standards for the Ore Mining and Dressing
Point Source Category," EPA Report No. 440/1-82/061,
November, 1982.
3. Harty, D.M. and Terlecky, P.M., "Reconnaissance Sampling and
Settling Column Test Results at Alaskan Placer Gold Mines,"
Frontier Technical Associates Report No. FTA-84-1402-1.
4. Kohlmann and Ruggiero Engineers, "Treatability Testing of
Placer Gold Mine Sluice Waters in Alaska, U.S.", Prepared
for USEPA Effluent Guidelines Divison, January, 1984.
5. R&M Consultants, Inc., "Placer Mining Wastewater Settling
Pond Demonstration Project", Prepared for the Alaska
Department of Environmental Conservation, June, 1982.
6. Environment Canada, "The Use of Flocculants in Placer
Mining" (a supplement to the paper 'The Attainment and Cost
of Placer Mining Effluent Guidelines'), Canadian
Environmental Protection Service, Yukon Branch, June 13,
1983.
7. Canadian Department of Indian and Northern Affairs, "Water
Use Technology for Placer Mining Effluent Control," Report
No. QS-Y006-000-EE-A, 1981.
8. Bainbridge, K.L., "Evaluation of Wastewater Treatment
Practices Employed at Alaskan Gold Placer Mining
Operations", Report No. 6332-M-2, Calspan Corporation,
Buffalo, N.Y., July 17, 1979.
9. USEPA National Enforcement Investigations Center,
"Evaluation of Settleable Solids Removal Alaska Gold Placer
Mines", EPA Report No. 330/2-77-021, September, 1977.
VII-15
-------
10. Alaska Department of Environmental Conservation, "Placer
Mining and Water Quality" (Summary Report), November, 1979;
Supplements: Problem Description-Nov. 1977; Technical
Alternatives-June 1978; Management Alternatives-Sept. 1978.
11. Dames & Moore, "Water Quality Data at Selected Active Placer
Mines in Alaska" Report No. 9149-001-22, September 17, 1976,
prepared for Calspan Corporation.
12. Kohlmann Ruggiero Engineers, "1984 Alaskan Placer Mining
Study and Testing Summary Report," Revised November 8,
1984, Preliminary Draft, Prepared for EPA Effluent Guide-
lines Division, Washington, D.C.
13. Shannon and Wilson, Inc. "Placer Mining Wastewater
Treatment Technology Project Phase 1, 2 and 3 Report,"
Prepared for State of Alaska Department of Environmental
Conservation, November 1984.
VII-16
-------
SECTION VIII
CONTROL AND TREATMENT TECHNOLOGY
This section discusses the techniques for pollution abatement
available to the placer gold mining industry. General categories
of techniques are: in-process controls, end-of-pipe treatment,
and best management practices. The current or potential use of
each technology in this and similar industries and the
effectiveness of each are discussed.
Selection of the optimal control and treatment technology for
wastewater generated by this industry is influenced by several
factors:
1. There are some differences in wastewater composition
and treatability caused by ore mineralogy, ore particle size and
distribution, and processing techniques.
2. Geographic location, topography, and climatic
conditions often influence the amount of water to be handled,
treatment and control strategies, and costs.
3. Seasonal nature of the operation where mines operate
only during the mining season often causes a mine operator to
rebuild the treatment facility each season the mine is operated.
In-Process Control Technology
This section discusses process changes available to existing
mines to improve the quality or reduce the quantity of wastewater
VIII-1
-------
discharged from mines. The techniques are process changes that
may be made within existing mining operations.
1. Classification or Screening
Mines which employ classification (sizing or screening) of the
ore prior to sluicing typically use less water than mines which
do not classify. Several different classification devices are
commonly employed at placer gold mines. These devices are
trommels, screens (fixed and vibrating), and grizzlies. Each of
these devices removes oversized material prior to sluicing.
Removal of oversized material reduces water usage because less
material is sluiced and a lower water velocity is required to
push the smaller rocks down the sluices. Descriptions of
trommels, screens, and grizzlies are found in Section III.
Estimated water use rates for each of the classification devices
and for mines using no classification are shown in Table VIII-1.
Average water usage at mines employing classification methods
(screens, trommels, and grizzlies) is approximately 2,500 gallons
per cubic yard (9.5 m3 of water per m3 of paydirt). At mines
using no classification, the average water usage is 4,062 gallons
per cubic yard (15.4 m3/m3). Based on these water usage rates,
classification reduces water usage, and the volume of wastewater
for treatment, on the average of approximately 38 percent.
Classification or screening is common practice in the industry
because of mines in water short areas and many operators consider
it good mining practice which not only reduces water use, but
protects the sluice from the hammering of large rocks. In
VIII-2
-------
Table VIII-1. Water Use Rates at Placer Gold Mines
(Source: Reference 1)
Water Usage ga/cu. yd.)
Class. Method
Mines
Avg
Screens (Vib. &
ROSS Box)
Trommels
Trommels (Excl.
Dredges)
Grizzlies
No Classification
8
9
6
9
10
2,901
1,981
1,054
1,884
4,062
Range
947 to 6,000
209 to 7,411
209 to 2,400
1,440 to 3,360
900 to 8,970
Avg. Water Use—All Classification Methods Combined = 2,498.5
or approx. 2,500 gal/cu. yd. sluiced
VIII-3
-------
Section III, table 4 to 8, over 50% of the mines use some form of
classification.
2. High Pressure - Low Volume Spray Nozzles
The amount of water required at gold placer mines is affected by
the cohesiveness of ore particles. Mines washing ores which
contain cohesive clay particles generally use significantly
greater volumes of water to break up the ore during beneficiation
than mines washing ores with larger particle sizes and less clay.
Screening in conjunction with high pressure, low volume spray
nozzles before the separation process can assist in breaking up
the agglomerated paydirt into particles and use less water than
large volume hydraulic monitors.
3. Sluice design
Water usage in the sluice is a function of slope, width, water
depth, riffle type, riffle spacing, and ore particle size as
discussed in 2 above and size distribution of the ore as
discussed in 1 above under classification. However, sluice design
and the efficiency of a given sluice in recovering gold is most
often the result of trial and error by the miner to obtain the
best recovery of gold from a particular paydirt. It is beyond
the scope of this document to make specific recommendations other
than the two suggestions in 1 and 2 above that should be used
universally in designing and operating a sluice. Mining texts
and handbooks offer rules of thumb which the more efficient miner
customizes and perfects to the individual operation, including
controlled water use.
VIII-4
-------
4. Flow Control
Water use in the sluice at many mines can be reduced by stopping
the influent flow to the beneficiation process during extended
periods when ore is not being loaded into the process thereby
decreasing the total flow into the settling ponds and increasing
the settling time.
END-OF-PIPE TREATMENT TECHNOLOGIES
This subsection presents a discussion of technologies which may
be employed for the treatment of wastewater discharged at placer
mining operations. Most mines are in remote locations, so that
the type of equipment and the availability of outside
construction services must be considered. For a given site, the
terrain is most important to define design, construction and
maintenance requirement for treatment facilities. The following
factors were also considered in reviewing the available and
appropriate treatment and control facilities for gold placer
mines.
1. Engineering considerations for construction of
treatment facilities in most mining locations, including settling
pond size, number of ponds, drainage diversion, water use
reduction.
2. The length of the mining season which ranges from about
four (4) months in Alaska to 5-10 months in the Western States.
3. Design considerations due to climate, especially
rainfall.
VIII-5
-------
4. Construction equipment available to, and practices
employed by, the mining crew to install treatment or control
facilities.
The ore industry currently uses some form of sedimentation
technology which involves generally one of the following:
settling basins, clarifiers, or ponds. Large concrete settling
basins and clarifiers normally found at typical "hard rock" ore
mines are generally not found nor adaptable to conditions related
to seasonal operation and the remote location of placer mines.
These conditions, combined with the treatability of wastewater
and the costs of treatment make many wastewater treatment
technologies that are used at some other ore mining operations
impractical at placer mining operations. These include granular
media filtration, adsorption, chemical treatment, and ion
exchange.
Technology Description
Simple Settling
The use of ponds for both primary or secondary settling is a
standard approach to treatment throughout the ore mining industry
and in particular for placer mining. The wastewater entering
these ponds from the mining and ore processing operations contain
a high solids loading. Primary settling ponds are often used to
remove the heavy particles and then secondary settling ponds are
used to remove the finer particles.
VIII-6
-------
The size of settling ponds is determined by the overflow rate or
detention time needed to remove the solids. In general,
detention time is used to determine the pond size in the mining
industry. Engineering tests at several sites in Alaska during
1983 and 1984, using quiescent settling conditions, revealed that
the largest portion of suspended and settleable solids removal
occurred during the first 2 to 3 hours of settling.(13)
Additional settling beyond three to six hours, while assuring
removal of any residual settleable solids, does not greatly alter
the removal of suspended solids from the wastewater.(13) Based on
the data obtained in pilot settling tests, engineering
requirements and experience for design and construction of actual
field installations, doubling the settling time (i.e., 3-hrs
pilot test vs. 6-hr, field design) would be required to
compensate for flow velocities and sludge storage in the pond.
DESIGN CONSTRUCTION AND OPERATION OF SETTLING PONDS
To achieve the desired results or effluent from a settling
pond(s), the pond must be properly designed, installed and
maintained. It was apparent from the visits to many mine sites
that ponds which were installed although of sufficient volume at
the beginning of the mining season, due to accumulation of
sludge, were of insufficient size to treat the wastewater later
in the season. Also, the ponds at some mines visited were
"short-circuiting" (i.e., wastewater flowed straight through the
pond without much, if any settling) due to improper placement of
the influent and effluent points.
VIII-7
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A properly designed pond should have the influent in the middle
of one end and the effluent at the middle of the other end.
Ideal ponds have the length two (2) to three (3) times the width,
and adjustable weirs at the influent and effluent points. These
weirs are utilized to determine the flow into and out of the
ponds and to control water height in the ponds.
The disposal of sludge deposited in the ponds can be handled by
two methods. (1) Sludge can be removed from the ponds
periodically, using mechanical means such as dredges, slurry
pumps, front end loaders, back hoes or dredge lines, and disposed
in the area used for tailings disposal; or (2) sludge can be left
in the pond for the entire season. Both approaches require the
pond volumes to be increased above that required for detention of
the wastewater being treated so that the volume of sludge does
not intrude on the volume required for proper wastewater
detention and treatment. The increased volume of the ponds will
depend upon the method of sludge disposal being utilized, and the
amount of solids present in the wastewater that will settle. The
ponds will be smaller in volume if the sludge is removed
periodically.
Therefore, sizing the settling pond for a mine site the following
must be determined.
1. Volume of wastewater to be treated
2. Amount of sludge to be handled
3. Method of sludge handling.
VIII-8
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Using this data ponds of proper size to treat the wastewater
generated can be designed and installed.
DETERMINATION OP WASTEWATER VOLUME TO BE TREATED
The volume of wastewater to be treated in placer mining
operations is determined from: (1) the actual amount of water
used in the beneficiation process (sluicing); (2) the amount of
ground water or infiltration which enters the pond; (3) the storm
water runoff from the beneficiation process area and the mine
area for a given storm intensity1 which enters the pond; and
(4) the water flow from any other sources, i.e., small creeks,
which are not diverted around the ponds but enter the ponds. The
waters from these four sources are combined to produce the total
volume of water used to size the treatment ponds.
The size of the ponds and cost of construction discussed in
Section IX are based on the volume of water to be treated. At
most mine sites the major flow to be treated is the process waste
water used for beneficiation process, i.e., sluicing. Minimizing
process wastewater use by high pressure, low volume nozzles for
pre-wash, and ore classification will result in smaller ponds and
lower costs for treament of process wastewater.
^As discussed in Section X, relief or an exemption is
provided to wastewater treatment facilities which are overcome by
storm water runoff if the treatment facility is designed,
constructed, and operated to contain or treat the volume of
wastewater that would result from a 5-year, 6-hour rainfall.
Therefore, the 5-year, 6-hour rainfall should be the storm
intensity used.
VIII-9
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DETERMINATION OF SLUDGE VOLUME TO BE HANDLED
The volume of sludge is computed by determining the amount of
suspended solids present in the wastewater entering the pond and
the amount of suspended solids present in the wastewater
discharging the pond after the required settling time. Using the
difference between the influent and effluent suspended solids and
the volume of wastewater being treated, the amount of sludge to
be handled can be computed. Using this data and the methods of
sludge handling, the volume of the pond required for sludge
storage can be determined.
POND DESIGN EXAMPLE
An example of the sizing of a pond at a placer mining site is
offered below:
A. Design Criteria
1. Flow: Flows are mine specific and only the
process wastewater is considered in this example.
The sluicing water rate is based on an assumed
rate of sluicing 80 cubic yards per hour (or 800
cubic yards per day for a 10-hr day) using an
assumed 2500 gallons of water per cubic yard.
The wastewater discharging the sluice would be
about 3,400 gpm.
2. Detention time for wastewater: 6 hours
VIII-10
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3. Maximum pond velocity to avoid scouring
("critical velocity") should be about 2 feet
per minute or less.
4. Sludge volume is based on an influent quality
of 30,000 mg/1 and an effluent quality of
2,000 mg/1 of total suspended solids. Sludge
on the pond bottom is assumed to have 50
percent solids.
5. For the purpose of this example, the sludge will
remain in the ponds for the entire mining season.
Assume 100 days of sluicing at 10 hours per day.
B. Detention
The volume is computed by multiplying the flow by the detention
time required and converting to cubic feet by dividing the
results by gallons per cubic feet.
Volume = 3,400 x 6 x 60/7.48 = 164,700 cubic feet.
C. Cross-section and Surface Areas
These are determined by trial and error to achieve the dimensions
suitable for a mine site.
Assume a depth of 3 feet. Surface area required is:
164,700/3 = 54,900 square feet.
Using a length to width ratio of 2.5 to 1, the width would be 150
feet and the length: 375 feet.
VIII-11
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D. Check Critical Velocity
Convert flow to cubic feet per second.
Divide flow by 448: 3400/448 = 7.59 cfs.
Divide by crossectional area: 7.59/150 x 3 = 0.02 fps,
which equals 1.0 fpm, e.g., below critical velocity.
E. Sludge Determination
Subtract effluent suspended solids from influent suspended
solids:
30,000 - 2,000 * 28,000 mg/1 remaining in pond.
Using this volume and flow, the amount of solids is computed for
the mining season:
(28,000 x 3400 x .012 x 10/24) x 100 = 47,600,000 pounds per
year.
Assume 50% solids in the sludge, the volume of the pond to
maintain this sludge can be determined. For this example, the
volume for sludge storage for the year is:
47,600,000 x .5 = 1,525,641 cubic feet
62.4
Based on this example, a pond or ponds having a usable volume for
the combined total of water volume and the sludge volume, that is
1,580,541 cubic feet, or 58,539 cubic yards, must be constructed.
VIII-12
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This pond would provide the required detention time for the
process wastewater and volume for a mining season's sludge
production, while achieving a settleable solids level of less
than 0.2 ml/1 as determined from treatability testing of simple
settling.(13)
Coagulation and Flocculation
The majority of the suspended solids present in placer mine
effluent from simple settling are colloidal in size and do not
readily settle without the aid of chemicals. In general, two
types of chemicals are used in the treatment of waters: those
that precipitate materials from solution (e.g., lime), and those
that coagulate small particles into particles large enough to
settle by gravity or be removed by other physical methods. The
major chemicals used for coagulation are organic or inorganic
materials (polyelectrolytes). Polymers operate by forming a
physical bridge between particles, thereby causing them to
agglomerate forming a floe. The floe, e.g., agglomeration of
small particles, is generally settleable. When the
polyelectrolyte alone does not form particles that will settle
due to lack of ample weight, coagulant aids such as lime or
ferric sulfate are used to add the required weight.
Coagulant aids are normally added ahead of the settling facility.
The coagulant or polyelectrolyte must be added and mixed with the
wastewater by an action such as turbulence to ensure complete
mixing and dispersion of the coagulant into the wastewater.
After complete mixing, the wastewater treated with polymer must
VIII-15
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pass through a flocculation stage which allows the particles to
come in contact with each other so that the agglomeration can
occur to form a floe.
The use of flocculant system at a mine site can be relatively
simple operation. A polyelectrolyte feed system would be
installed prior to the settling pond. The feed system would be a
batch type operation where the polyelectrolyte solution is
prepared daily and a metering pump is utilized to feed the
solution into the wastewater.
Table VIII-2. Summary of Two-hour Settling Tests Performed
During the 1984 Testing Program*
Polymer Aided Settling
Mean Value Range
0.0 - Trace
8-62
19 - 185
<0.002- 0.089
0.0005
Parameters
Settleable solids (ml/l/hr) Trace
Total suspended solids (mg/1) 25
Turbidity (NTU) 88
Total mercury (mg/1) 0.019
Total arsenic (mg/1) <0.0005
*Extrapolated from plots of field data
If a turbulent (mixing) area is not present prior to the settling
pond, a section to create turbulence can be constructed, a
serpentine channel or placing constrictions in the channel that
will cause turbulence.
Settling tests in Alaska during the 1983 mining season confirmed
the use of polyelectrolytes as a method to treat placer mining
wastewater and the 1984 tests confirmed the viability of treating
VIII-16
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placer mining wastewaters with polyelectrolyte.(12 and 13) The
1983 testing was utilized to determine the feasibility of using
polyelectrolyte in the treatment of placer mining wastewaters and
the 1984 testing program was designed to determine the quality of
water discharging ponds at various detention times and determine
the optimum dosage of polyelectrolyte. The 1984 testing program
consisted of running several two-hour settling tests and at least
one long-term (24-hour) settling test at each site. Table VIII-2
present summaries of the 1984 testing program.
Natural Filtration
Removal of solids by filtration is achieved by passing the
wastewater through a medium where the pore sizes are smaller than
the particles being removed, thereby trapping the particles. At
many placer mines, filtration is performed naturally as the
wastewater is discharged through the tailings from the mining
operations. Those particles larger than the pore size in the
tailings are trapped and removed. Tailings filtration may be
beneficial in that the fines are recombined with the coarse
tailings. No specific data are available to determine the
removal efficiencies or the effluent quality from existing
treatment at placer mines because the discharge is not generally
discrete, but is most often diffuse in the form of seepage.
Recycle of_ Process Waters
A major method of reducing the pollution load on the receiving
waters is the recycling of process water. This also conserves
VIII-17
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water and is a present practice at many placer mines.
Approximately 50% of the mines recycle all or a portion of their
wastewater. Recycling of process waters at a placer mine is a
relatively simple operation, requiring the installation of a pump
at the pond and piping to the head of the mining operation. The
size of the pumps and piping would be based on the process flow
required and the percentage to be recycled.
Recycling of wastewater at gold placer mines has several
advantages and disadvantages as summarized below:
Advantages
Allows mining especially
in water short areas and
minimizes water use
elsewhere.
Disadvantages
Reduces mass of pollutant
load to the receiving
stream.
2.
Higher pumping costs are
incurred because of
additional energy
requirements and
expected increased
pump wear.
Higher piping costs
because more pipe may
be required, additional
wear on the pipe and
steel pipe may be
required in place of
plastic pipe.
3. Smaller or fewer settling
ponds may be required to
meet effluent limitations,
A concern of the industry is that fine gold recovery decreases
when recycled water containing suspended solids is reused in the
sluice. However, only limited scientific data were available to
address this issue. Therefore, the Alaska Department of
Environmental Conservation (ADEC) funded a study (Reference 3) to
address the potential loss of gold recovery during recycle. This
VIII-18
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FIGURE 3
PILOT TEST
RECYCLE FACILITY
(PLAN VIEW)
seal*: !/*'• r
V
Hand-Held
Wash Hose
Wash Water
Control Valve
Spray Bar Water
Control Valve
Recycle
Pump
Recycle Water
Pump Intake
Three-Comportment
Water Tank
VIII-19
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VIII-20
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study was divided into two parts, a pilot-scale study and a field
study. EPA expanded on this study and funded a supplemental
study on the effects of recycle on gold recovery. The EPA study,
Reference 4, used essentially the same set-up as the ADEC study.
In both of these studies, a six-inch-wide, eight-foot-long sluice
with a feed hopper and slick plate were used (see Figure VIII-3
and Figure VIII-4). The slope of the sluice during both studies
was set at 1.75 inches per foot.
In the EPA-funded study, ore from an operating mine in the
Fairbanks District was used. The paydirt was screened and only
material finer than 0.75 inch was used in the pilot-scale tests.
A new batch of ore with an unknown quantity of gold was used
during each run. The material was resluiced after each run to
determine the gold loss. The gold used in the study was -30 to
+60 mesh. A known quantity of gold was added to the ore prior to
each run in order to have a statistically significant amount of
gold in the sluice box. The target TSS levels in the test runs
were as follows:
Table VIII-3
Test No. TSS Concentration (mg/1)
1 0
2 25,000
3 50,000
4 100,000
5 200,000
6 200,000
The size distribution of gold added during each test run is shown
in Table VIII-4. The major results of this study are summarized
on Tables BIII-5 and VIII-6. At all suspended solids
VIII-21
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Table VIII-4. Size Distribution of Gold Added to Each Run.
Run No.
1
2
3
4
5
6
Total
-30 + 50
Mesh
9.9612
10.0079
10.2561
10.3743
9.8473
10.2897
-50 + 60
Mesh
2.5279
2.6490
2.4956
2.5238
2.6621
2.5169
Total
12.4891
12.6569
12.7517
12.8981
12.5094
12.8066
60.7365
15.3753
Note: Amounts of gold are presented in grams.
Source: Reference 4
76.1118
VIII-22
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Tfb.le VIIl-5. Pilot Test Water Quality Data (Sluice Influent).
t,
SLUICE INFLUENT
Run
Parameter
Suspended solids
Turbidity
Settleable Solids
Specific Gravity
Viscosity @ 20°C
Vise. 6 Run Temp.
Run Duration
Water Duty
SLUICE EFFLUENT
123456
10,000 48,000 65,100 98,300 199,000 204,000
2,200 24,000 33,000 39,000 128,000 100,000
1
217-
95
-0.1
0.998
1.0 ;
2.0
34 .
0.22 .
2
39,100'
24,000
180
1.022
1.8
3.2
39
0.19
3
58,800
30,000
270
1.034
2.0
2.9
37
0.21
4
90,100
46,000
400
1.052
3.0
4.9
38
0.20
' 5
194,000
134,000
680
1.122
4.2
7.7
38
0.20
6
187,000
108,000
650
1.118
4.1
6.2
14
0.56
Suspended Solids
Turbidity
Settleable Solids
Specific Gravity
Viscosity @ 20°C
Vise. @ Run Temp.
Units:.. Suspended Solids mg/L
Turbidity NTU
Settleable Solids ml/L
Specific Gravity gm/cc at 20° C
Viscosity
Run Duration
Wa t ur Du t y
25
1.004
1.5 .
3.0
200
1.029
1.7
3.1
290
1.039
2.2
3.1
420
1.060
2.8
4.6
680
1.122
4.4
8.1
660
1.133
4.9
7.3
cp(centipoise) - gm mass/cm sec
min
ydVlOOO 9*1 (cubic yards of pay dirt
,sluiced using 1000 gallons of water)
Note: '"-0.1" denotes less than 0.1
Source: Reference 4
VIII-23
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Table VIII-6. Percent Gold Recovery.
TOTAL GOLD
Riffle
Run
1
2
3
4
5
6
Run
1
2
3
4
5
6
1
99.63
99.59
99.54
99.40
99.08
97.84
1
99.00
98.97
98.96
98.41
97.96
95.42
2
0.32
0.38
0.39
0.52
0.71
1.83
-50
2
0.81
0.94
0.86
1.41
1.79
4.03
3
-0.01
0.02
-0.01
0.04
0.04
0.08
+ 80
3
0.02
0.05
0.03
0.06
0.10
0.25
4
0.01
0.01
-0.01
0.03
0.03
0.08
MESH GOLD
Riffle
4
0.05
0.02
0.04
0.08
0.04
0.09
Gold Loss*
0.04
-0.01
0.05
0.02
0.13
0.18
Gold Loss*
0.12
0.03
0.11
0.04
0.11
0.21
Note: "-0.01" denotes less than 0.01 percent,
*Recovered after sluicing by suction dredge
Source: Reference 4
VIII-24
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VIII-26
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concentrations, over 99.5 percent of the gold was recovered. The
results of this study and the ADEC study indicate that gold loss
due to recycle is minimal.
Recycle Practices at Alaska Placer Gold Mines. Recycle pratices
at various production levels were investigated (5). It was
determined that partial and 100 percent recycle are practiced at
all mine sizes; however, approximately one-half (50.7 percent) do
not recycle any process wastewater.
Table VIII-7 lists the number of mines recycling wastewater,
grouped by production level and the amount of recycle employed.
Table VIII-8 lists the percentage of mines practicing recycle by
percentage of recycle. This information was derived from
Reference 5 and was obtained from a computerized summary of Tri-
Agency Forms compiled from mines which submitted completed Tri-
Agency Forms in 1984. These forms are submitted by the miner
prior to the mining season and are an estimate of what the miner
intends to do, not necessarily what will actually be done. The
table below summarizes the Alaskan gold placer industry by
production level from information submitted on Tri-Agency Forms.
Table VIII-9
<1000 1000 to 2500 >2500
Mines 81.6% 13.0% 5.4%
Production 34.5% 29.9% 35.6%
VIII-27
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The larger mines are small in number but sluice approximately
one-third of the total volume of material. Based on production
levels above, 21.3 percent of the industry is achieving 90-100
percent recycle of the process wastewater.
Geographic Distribution of Mines Which Recycle. The geographic
distribution of mines practicing some degree of recycle was
examined to determine if location played any significant role in
determination of recycle practices. The table below summarizes
the approximate percentage of mines in each mining district and
the corresponding percentage of partial and total wastewater
recycling operations (Reference 6):
Table VIII-10
Percentage of Percentage of
Mining District Mines Recycling Mining Operations
Circle 15.4 17.5
Fairbanks 26.4 24.2
Forty Mile 7.3 7.2
Hot Springs 1.8 1.3
Iditarod 0.0 0.9
Innok 0.9 0.0
Koyukuk 6.4 6.3
Kuskikwin 3.6 2.3
Seward 2.7 4.6
Seward Peninsula 6.4 4.0
Other Districts 29.1 30.9
Based upon the analysis presented above, recycling of wastewater
at placer gold mines in Alaska is practiced in all major Alaskan
mining districts. Many facilities which recycle do so because of
limited water availability.
VIII-28
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Treatment System Options
After a review of available data, it is apparent that treatment
of placer mine wastewater should be based on the use of simple
settling with or without recycle or polymer addition to the blow
down from recycle. The settling ponds should be sized for six
hours detention time. In addition, the pond should have a volume
sufficient to store the amount of sludge expected without
interfering with the detention time. In evaluating the use of
primary and secondary settling ponds, polyelectrolyte use and
recycling, several arrangements and points of polyelectrolyte
application were considered. After an in-depth review of
potential systems, five alternative treatment systems are being
considered. These systems or options are presented schematically
on Figure VIII-5 through VIII-7.
Option 1^
This option consists of using one primary pond. The pond would
be sized for six hours detention time of process water plus 20
percent for freeboard, and the volume necessary to store the
expected sludge volume.
Option j2
This option utilizes two settling ponds, primary and secondary.
The primary pond, designed to settle the heavy particles, would
be sized for one hour detention time of process water. Flow from
the primary pond would be further treated in a secondary pond
sized for six hours detention time for the process water. This
VIII-29
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FIGURE vm-5 ;PLACER MINING WASTEWATER TREATMENT OPTIONS
INFLUENT
PRIMARY.
SETTLING
DISCHARGE
OPTION 1
INFLUENT
PRIMARY
SETTLING
SECONDARY
SETTLING
DISCHARGE
OPTION 2
VIII-30
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FIGURE VIII 7.6.-: PLACER MINING WASTEWATER TREATMENT OPTIONS
INFLUENT
REUSE ,*.
PRIMARY
SETTLING
SECONDARY /|
SETTLING
RECYCLE PUMP
DISCHARGE
INF; UENT
OPTION 3
FLOCCULANT
ADDITION
PRIMARY
SETTLING
1
n^k
SECONDARY 1
SETTLING 1
'RECYCLE PUMP
OPTION 4
DISCHARGE
VIII-31
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FIGURE VI11-7. PLACER MINING WASTEWATER TREATMENT OPTIONS
INFLUENT
REUSE
PRIMARY
SETTLING
RECYCLE PUMP
OPTION S
VIII-32
-------
approach allows for the construction of a small primary pond near
the mining operation which would be reconstructed as the mining
area moves, and the construction of a larger secondary pond once
a season to treat all the process water.
Option 3i
This option employs the same two-pond system as Option 2 but
includes recycle after the primary pond. The primary pond would
be sized for one hour detention of process water. Eighty percent
of the water would be returned to the beneficiation process for
reuse and the remainder (the 20 percent blowdown) would be
further treated in a secondary pond. The secondary pond would be
sized for the blowdown on that portion of the wastewater not
recycled. This approach would reduce the pollution load or the
mass of pollutants to the receiving water by eighty percent due
to recycle.
Option £
This option is the same as Option 3, except that a flocculant aid
(polyelectrolyte) is added between the primary and secondary
ponds after the water has been recycled. Again the pollution
load to the receiving water would be reduced because of recycle
as in Option 3 and the use of polyelectrolyte on the blowdown
would further reduce the pollution load to the receiving water
over the reduction obtained by Option 3.
VIII-33
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Option 5^
This option is the same as Option 1, using one primary pond as a
holding pond, but the total volume of process water is recycled.
This option would have no discharge of process wastewater from
the beneficiation process.
HISTORICAL DATA SUMMARY
As discussed in Section V, the EPA data base consists of 16
studies and sampling and analysis programs from 197(5 to 1984.
Additional studies and analysis are being performed now and more
will be conducted in 1986. Below is a summary of the data
gathered during seven studies conducted by EPA, Alaska Department
of Environmental Conservation, their contractors and the Canadian
Department of Indian and Northern Affairs. Data from many
different facilities over several years have been collected.
However, as summarized below and as can be found in the
individual reports, the data for existing facilities prior to
1984 was not adequate to propose effluent limitations guidelines
and standards. Therefore, EPA is relying primary upon the data
and information obtained in 1984 studies of existing treatment,
interpretation of pretreatment studies and the engineering
assessment of the basic treatment process to propose effluent
limitations and standards.
Dames and Moore Study - 1976
This study was one of the first studies conducted which attempted
to evaluate water quality from mining operations (7). Many of
VIII-34
-------
the mines visited did not have settling ponds installed, and
therefore little information on the effectiveness of settling
ponds was obtained.
NEIC Study - 1977
The EPA National Enforcement Investigations Center sampled eight
mines with ponds (8). The effluent water quality from the single
or multiple pond settling systems is summarized in Table VIII-11.
The results indicate a wide range of settleable solids levels
achieved ranging from <0.1 to 15 ml/1. Mercury was not detected
in the effluent from any of the settling ponds. The ponds are
characterized as not being designed or built to obtain effluent
goals, but to provide a temporary holding pond or sump for
process water for the beneficiation process, i.e., sluice.
Calspan Study - 1979
In 1978, Calspan Corporation sampled the effluent from eleven
operating Alaskan placer gold operations (9). The effluent data
from the ten active mining operations with settling ponds are
summarized in Table VIII-12. Five mines achieved settleable
solids readings of less than 0.1 ml/1. The total suspended
solids (TSS) concentrations ranged from 76 to 5,700 mg/1 in the
effluent. No turbidity readings were obtained. Arsenic
concentrations in the final effluent ranged from <0.002 mg/1 to
1.2 mg/1. It was noted that the highest settleable solids and
TSS readings occurred with the highest arsenic and mercury data
which suggested a concentration of TSS with arsenic and mercury.
VIII-35
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Table VIII-11. Historical Data Summary from NEIC Study - 1977.
Settling Pond Effluent Data*
Settleable
Mine Solids
Code (ml/l/hr)
4139
4114
4140
Unknown
4107
4141
4134
4142
15
NA
1.3
<0.1
NA
<0.1
0.4
0.3
Total
Turbidity
(NTU)
1,200
140
740
130
5,200
79
1,300
1,800
TSS
(mg/1)
4,000
NA
1,000
220
22,000
120
1,420
2,080
Total
Arsenic
(mg/1)
0.560
NA
NA
0.057
2.5
0.031
0.280
0.270
Total
Mercury
(mg/1)
<0.0001
NA
NA
<0.0002
<0.001
<0.0002
<0.0002
<0.0002
*Two additional mines sampled, however no pond effluent samples were
obtained.
NA - Not Analyzed
VIII-36
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Table VIII-12. Historical Data Summary from Calspan Study - 1979,
Settling Pond Effluent Data*
Mine
Code
Settleable
Solids
(ml/l/hr)
<0.1
2.5
0.4 to 0.8
<0.1
0.3 to 0.42
1.5 to 2.8
0.7 to 0.9
<0.1
<0.1
<0.1
TSS
(mg/1)
57
5,700
1,040
170
1,620
1,770
474
150
262
235
Total
Arsenic
(mg/1)
0.250
1.20
0.050
0.060
0.050
0.080
0.022
<0.002
<0.002
0.010
Total
Mercury
(mg/1)
<0.0002
0.0005
<0.0002
0.0002
<0.0002
<0.0002
<0.0002
<0.0002
<0.0002
<0.0002
4126
4127
4132
4133
4134
4144
4135
4136
4137
4138
*One additional mine was sampled, however there were no settling
ponds at this mine.
VIII-37
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Pond retention time and volume were not measured, but the visual
assessment indicated inadequately sized ponds are included in
this data.
R £ M Consultants Study ^ 1982
The R & M study included an evaluation of a demonstration pond,
settling column tests, and a reconnaissance study (10). R & M
Consultants visited and sampled seven mines employing settling
pond treatment technology. The effluent from these ponds was
sampled, and the results are presented in Table VIII-13. Ponds
sampled do not necessarily represent adequately sized ponds.
Therefore, the results do not indicate the best effluent quality
that can be achieved. Settleable solids concentrations ranged
from <0.1 to 19.5 ml/1. At one mine, an increase in settleable
solids, turbidity, and TSS increased during the year indicating
that the pond was filling up. Turbidity readings in the pond
effluent during this study ranged from 160 to 6,900 NTU and
averaged 2,676 NTU.
B. i M Treatability Study - 1982
One of the major objectives of the R & M study was to evaluate
the sedimentation rates of particles from placer mine sluice
discharges (10). Settling column tests were conducted on the
wastewater from 15 individual mines. Wastewater was obtained
from sluice box effluents. Turbidity values were taken 1.5 feet
and 5.5 feet below the initial height of the settling column.
The R & M study concluded "that reductions in turbidity to the
Alaska standard of 25 NTU above natural conditions could probably
VIII-38
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Table VIII-13. Historical Data Summary from R&M Reconnaisance
Study - 1982.
Settling Pond Effluent Data
Settleable
Mine Trip Solids Turbidity TSS
Code No. (ml/l/hr) (NTU) (mg/1)
2 1 <0.1 1,100 776
2 Ponds Washed Out
3 Ponds Washed Out
3 1 <0.1 1,400 776
2 <0.1 850 468
3 0.1 1,300 600
6 1 0.1 1,400 910
2 <0.1 1,500 878
3 <0.1 1,100 1,180
8 1 No ponds during this visit
2 18 5,000 19,900
3 2 2,100 2,310
9 1 1.7 1,800 1,090
2 5.5 4,000 2,070
3 19.5 NA NA
13 1 <0.1 1,800 660
2 <0.1 160 410
14 1 0.1 4,500 2,960
2 4.5 7,900 5,160
3 6.5 6,900 6,470
*Mine 1 not included since settling pond effluent samples were not
obtained. Mines 4, 5, 6, 10, 11 and 12 were not included since no
settling ponds were employed at these sites.
NA - Not Analyzed
VIII-39
-------
not be obtained in a practical manner by sedimentation alone." R
& M Consultants' extrapolation of the data indicated that
approximately 60 days of sedimentation would be necessary to
achieve the 25 NTU standard under the laboratory conditions of
the test. Based on the settling column tests, R & M concluded
that it would not be practical to design a demonstration settling
pond to achieve state turbidity standards.
A 22-day settling column test was conducted at one mine. After
528 hours of quiescent settling, the TSS and turbidity values
were 120 mg/1 and 390 NTU, respectively. Even after 22 days, a
considerable amount of dilution water from the creek would be
needed to meet the State of Alaska water quality standard for
turbidity.
At 15 mines, six-day settling column tests were conducted. The
average TSS concentration from the 15 mines after six days of
quiescent settling was 931.3 mg/1. The average turbidity reading
obtained at the end of the same period was 1,543.7 NTU.
KRE 1984 ^ Reconnaissance and Treatability Study
Kohlmann Ruggiero Engineers (KRE) gathered data during the 1984
mining season at gold placer mines in Alaska. Studies included
treatability tests of effluents with and without polyelectrolyte
settling aids, flow determination, sampling and profiling the
mine's equipment costs, physical layout, and wastewater treatment
system. The details of this study can be found in Reference 13.
VIII-40
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Mine sites were screened using available data from 1983 and
through discussions with EPA, Region X, Alaska DEC, individual
miners and miners' associations. Twenty mines were selected for
futher screening and on-site visits. These twenty mines were
selected to be representative of mines found over the State of
Alaska considering: geographical location, type of mining, size,
depth and type of overburden, topography, and treatment employed
(including high rate recycle).
These twenty mine sites were visited in June 1984 by EPA, KRE,
and a consulting mining engineer; an engineering work-up and fact
sheet was completed at each mine. The mines represented the 7
mining districts with the largest population of mines; mines had
capacities of 50 ydvday to over 3000 yd3/day; water use
varied from once-through to over 90 percent recycle; overburden
varied from none to over 60 ft; and mines located in broad flood
plains and narrow valleys were represented. The data collected
were reviewed by EPA-ITD and KRE, and ten mines were selected as
representative of the site factors considered. These ten mines
were than sampled and on-site treatability studies were
performed.
During the month of July and August 1984, a field crew from KRE
visited each of the 10 mines selected and conducted on-site
treatability testing as well as sampling and analyses for
settleable solids and turbidity. Samples were prepared for
laboratory analyses of TSS, arsenic, and mercury and flow
measurements were made at each of the 10 mines selected. The
VIII-41
-------
crew were on site two to four days at each mine.
At each mine, the treatability tests were performed in three
parts. First, jar tests were used to select the appropriate
polyelectrolytes and to determine dosage at each site. Second,
settling column tests, with and without polyelectrolytes, were
conducted over a period of two hours. Finally, a long-term (up
to 24 hours) unaided settling test was conducted.
The existing wastewater treatment system was evaluated by
sampling the influent water, effluent from the sluice, effluent
from the ponds or discharge to the receiving water, and other
points to evaluate water quality, i.e., recycle water and run
off. Using dye, flow patterns were observed to determine
detention time or identify short-circuiting in the ponds. Flow
meters or weirs were used to determine the flow from the sluice
and discharge from the ponds. The sizes of the ponds were
measured using a range finder and the depths were determined
using a "sinker" at various locations in the ponds.
Field observations by EPA personnel and contractors reveal that
properly designed, operated, and maintained settling ponds will
remove very high percentages of pollutants associated with the
solids encountered in the wastewater from placer mines. An
evaluation of the ten existing treatment facilities tested by KRE
in 1984 indicated that 4 of the mines should not be included in
the data base to determine effluent limitations because two of
the mines selected had not maintained the ponds and the ponds
were filled with sludge causing short circuiting and severly
VIII-42
-------
reduced detention time; one mine had no point source discharge
because of recycle; and one mine was identified as having an
unique distribution of collodial clays in the paydirt. For the
six mines remaining the arithmetic average of analysis are:
Averages (6 mines)
Water Sluice Final %
Supply Discharge Effluent Removed
Settleable Solids
(ml/1) 0.1 50 1.0 98.0
TSS (mg/1) 275 30,000 2,000 93.3
Turbidity (NTU) 300 22,500 4,000 82.2
Arsenic (mg/1) 0.0425 0.9000 0.3100 65.6
Mercury (mg/1) <0.0005 0.0070 0.0009 87.1
The installations used in the above tabulated averages are still
mixed in quality of basic design parameters (size, flow control,
and storage capacity for sludge resulting in reduced settling and
detention times), and operation and maintenance performance.
Based on observed conditions at the mines and at the mine's
treatment installations, two mines were identified as not having
properly designed, constructed, and maintained treatment systems
to serve as representative of best or even good treatment.
Eliminating the data from these two mines and averaging the
analysis from the remaining mines:
VIII-43
-------
Averages |4 best of 6)
Settleable
Solids (ml/1)
TSS (mg/1)
Turbidity (NTU)
Arsenic (mg/1)
Mercury (mg/1)
Water
Supply
0.10
275
300
0.0425
<0.0005
Sluice
Discharge
66
35,722
22,837
0.7364
0.0013
Final %
Effluent Removed
0.1
496
808
0.1288
<0.00()5*
99.9
98.6
96.5
82.5
61.5
*Results below the detection limit of 0.0005 mg/1.
The second phase of this 1984 field study consisted of performing
settling tests, e.g., plain settling without polyelectrolyte and
aided settling with polyelectrolyte. Jar tests were conducted to
identify the flocculant type and dosage. The results indicated
an optimal dosage of polyelectrolyte of about 2.0 mg/1.
VIII-44
-------
A combination of polymers in many instances proved more effective
in reducing the contaminant levels than application of a single
polymer. These tests are not all inclusive but offer a
comparison between plain settling and flocculant-assisted
settling. Numerical averaging is used below and all values
tabulated represent the average level after a detention time of
two hours.
Settleable
Solids (ml/1)
TSS (mg/1)1
Turbidity (NTU)
Arsenic (mg/1)
Mercury (mg/1)
Plain All Plocculant
Settling Assisted Tests
0.75
4472
9268
0.432
0.0057
85
375
0.0257
<0.0005
Best Flocculant
Assisted Test
Trace
24.7
88
0.0181
<0.0005
^Total suspended solids values (TSS) used to determine the
average after two hours settling are emperical observations taken
from the settling curves constructed for each individual test and
are conservativly high.(13) The TSS concentration in the actual
supernatant would be less than the value used here.
VIII-45
-------
These tests indicate a considerable reduction in solids can be
achieved by flocculant-assisted settling. The water samples at
the beginning of the tests and at the end of two hours were
analyzed for arsenic and mercury. These analyses for mercury and
arsenic indicate that mercury and arsenic are related to TSS and
are thus in the suspended or precipitated state and would be
removed incidentally with the removal of the suspended solids
(TSS) as discussed in Section VI.
In addition to the 2 hour settling tests, a 24 hour plain
settling test was performed on these same 10 mines. The
wastewater was sampled at 1 1/2 to 1 ft below the surface at 0,
1, 2, 3, 6, and 24 hours. As for the 2 hour settling test, the
solids in the supernatant would be consistantly less than
indicated here because the water was sampled well below the
surface of the testing device. A tabulation of these time
periods for the 10 mines is presented below.
Settling Settleable Suspended Solids Turbidity
Time-Hours Solids ml/1 mg/1 NTU
0 Range 3.2 to 125 5,580 to 51,413 2,016 to 34,560
Average 47.3 27,000 20,000
I Range 0.2 to 6 400 to 11,825 603 to 21,600
Average 1.75 6,600 10,000
2 Range 0 to 1.0 183 to 12,320 281 to 32,000
Average 0.47 5,200 11,300
3 Range 0 to 0.4 116 to 12,700 128 to 30,240
Average 0.16 4,900 9,950
6 Range 0 to 0.1 29 to 12,000 38 to 35,280
Average 0.05 3,900 9,650
24 Range 0 to <0.1 19 to 9,120 27 to 25,200
Average <0.1 2,800 7,700
VIII-46
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The results show a decrease in all parameters throughout the 24
hour period. Comparing the 2 hour test with the 24 hour test
results indicates the improvement from 6 hours to 24 hours is
minimal. Because of the obvious increased construction costs
(four times the volume) for the increased detention time of 6 to
24 hours, for design purposes, ponds to provide 6 hours of
detention time are used in the technology to attain effluent
limitations and to determine cost of construction.
In Section VI the long term, daily, and monthly achievable levels
are determined statistically using the effluent data obtained in
1984 at existing facilities sampled by EPA contractors and EPA
Region X sampling teams, and data from treatability studies
conducted by EPA contractors. As discussed above, some of the
effluent data from existing facilities does not represent good
treatment which can be obtained by properly designed,
constructed, and operated settling ponds. Also, by refering to
the data, i.e., total suspended solids analysis for the same day,
in Appendix VI-2 of Section VI, large differences in reported
values are observed which, if considered as individual values,
cause a large standard deviation from the mean and push up the
long term average. The effect of using data from under sized or
poorly constructed and operated treatment facilities is two fold:
(1) it increases the simple average or mean and (2) the peak
values, e.g., out liers, increase the statistically determined
attainable long term average limitations.
VIII-47
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EPA believes that simple settling facilities designed,
constructed, and operated as outlined in this section can
consistently attain less than 0.2 ml/1 settleable solids and less
than 2000 mg/1 total suspended solids as indicated by the KRE
1984 - Treatability Studies.
FTA and KRE Treatability Studies - 1983
The FTA and KRE treatability studies evaluated both unaided and
polymer-aided settling. The details of these studies are found
in References 12 and 13. Unaided settling column tests were
conducted at each of the eleven mines visited by FTA and KRE.
The results of unaided settling column tests have already been
summarized in Table VI-3.
Canadian Department of Indian and Northern Affairs
Treatability Study
The treatability studies performed for the Canadian Department of
Indian and Northern Affairs by Sigma Resources Consultants were
similar to both the FTA and KRE treatability studies. Unaided
and polymer-aided settling column tests and coagulation jar tests
using organic polymers were performed at several mines. Unaided
settling column tests were performed at four placer gold mines
and polymer-aided settling column tests were performed at two
mines. All mines were located in the Yukon Territory of Canada.
Settling column tests were performed on simulated sluice
effluents. Soil samples from the mine were mixed with a known
VIII-48
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volume of water to produce the simulated wastewater. A six-inch-
diameter, six-foot-long plexiglas column with sampling ports at
lf 3, and 5 feet from the bottom was used. Settling column tests
were performed to determine settling rates and settling pond
effluent quality. These settling column tests were conducted for
a period of 18 to 19 hours. Turbidity values at the end of
unaided settling tests ranged from 80 NTU to 2,200 NTU.
Two organic polymers, Superfloc 1128 and Separan MG 200, were
used in performing standard jar tests on simulated placer mine
wastewaters. Superfloc 1128 is a non-ionic polymer, which was
also used in the FTA treatability study. Separan MG 200 is an
anionic polymer. In this study, Separan MG 200 produced the best
results at each of the mines tested. Relatively low dosages of
this anionic polymer removed a high percentage of the turbidity
and suspended solids from the wastewater. Polymer dosages
between 3 and 20 mg/1 were effective. Jar tests at an additional
mine proved ineffective in that 20 mg/1 of Separan MG 200 was
required to produce a supernatant TSS of 500 mg/1.
Lime, alum, and ferric chloride were independently tested on this
wastewater at dosages of 100 mg/1. Using these inorganic
coagulants, TSS concentrations between 100 and 200 mg/1 were
achieved.
Based on the jar tests, two polymer-aided settling column tests
were conducted. The duration of these tests were relatively
short as most of the turbidity and suspended solids were removed
from the wastewater during the first few minutes of the test.
VIII-49
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Polymer dosages selected for use in the column tests were 3 mg/1
and 10 mg/1. At these dosages, final TSS concentrations of 30.5
mg/1 and 10.5 mg/1, respectively, were achieved.
In summary, this Canadian treatability study of Yukon gold placer
mine wastewaters supports the basic conclusions of the FTA, KRE,
and R & M treatability studies. First, unaided or natural
settling of gold placer mining wastewater over relatively long
periods of time does not produce a high quality effluent.
Secondly, several organic polymers have been identified which can
produce relatively low turbidity and suspended solids
concentrations in placer gold mining wastewater at dosages of
approximately 10 mg/1.
Best Management Practices
Section 304(e) of the Clean Water Act authorizes the
Administrator to prescribe "best management practices" ("BMP")
and Section 402(a)(l) of the Act allows the Administrator to
prescribe conditions in a permit which are necessary to carry out
the provisions of the Act including BMP's. The discharges to be
controlled by BMPs are plant site runoff, spillage or leaks,
sludges, or waste disposal and drainage from raw material
storage.
The gold placer mining industry has direct controls and
limitations on the storm water runoff which is mine drainage and
the groundwater infiltration and seepage which enters the
treatment system and is commingled with "process wastewater" as
discussed in Section X of this Development Document. Similarly
VIII-50
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the runoff from the "process area" discussed in Section X is
included in the "process wastewater" controlled by effluent
limitations guidelines and standards.
Minimizing the volume of water contaminated and going to mine
drainage is desirable because the volume of mine drainage and
mass of pollutants which is commingled to be treated is less.
Diversion of water around a mine site to prevent its contact with
the active mine and pollution-forming materials is an effective
and widely applied control technique at many ore mines.
Runoff
Runoff from outside of the mine area and groundwater seepage from
the surrounding hillsides should be diverted around the active
mining area at placer mines because this reduces the volume of
wastewater to be treated and can improve the performance of
existing treatment systems. For a given settling pond or group
of ponds as the volume of wastewater discharged into a pond
decreases, the retention time within the settling pond increases,
which increases the removal of settleable and suspended solids.
Control of the runoff from outside the active mining area is
practiced by many surface ore mines, but was not observed that
frequently at gold placer mines. Control technology or BMP's
include bypass ditches and berms to divert runoff away from the
mine which can be built using the mining and construction
equipment at the placer mine.
VIII-51
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Regrading and recontouring of the surface left after mining and
of the tailings and waste from the sluice can decrease surface
runoff going to mine drainage and also often decrease erosion of
the area after mining has ceased.
As mentioned above under in-process controls, influent to the
beneficiation process should be controlled or the flow stopped
during extended periods when the gold recovery process is not
being loaded. While it is a process control, it is also a best
management practice which reduces the leak of excessive
wastewater to the treatment system. Also, influent to the
process or make-up water to a recycle system can use mine
drainage rather than influent from the receiving stream which
will also reduce the amount of wastewater to be treated. The use
of mine drainage in the process as all or part of the required or
allowed influent is widely practiced by the industry.
As discussed above under design construction and operation of
settling ponds, sludge deposited in the ponds is generally
handled by mechanically cleaning the ponds periodically during
the mining season, by building a new pond as the old pond fills
with sludge and is left, or by building the original pond with
sufficient volume to hold the sludge produced in a season and
still provide sufficient retention time for the wastewater.
Regardless, the sludge produced in wastewater treatment should be
handled and disposed of in a manner which precludes through best
management practices the introduction of the sludge to the waters
protected by the effluent limitations. These practices include:
VIII-52
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1. Constructing the settling pond out of the stream and
out of the flood plain where practicable. Sludge left in the
pond will then have less probability of being washed out during
periods of heavy flow in the stream.
2. Sludge that is removed mechanically should be covered
and stored as far as practicable from the stream. Tailings from
the recovery process can be used to intermingle and to cover the
sludge.
3. Ponds that are to be abandoned at the end of the mining
season or are abandoned during the season because they filled
with sludge should be dewatered or drained to the interface of
the sludge and the ponds filled and leveled with tailings from
the recovery process.
VIII-53
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1. Harty, D. M. and Terlecky, P. M., "Water Use Rates at Alaskan
Placer Gold Mines Using Classification Methods," Memorandum to B.
M. Jarrett, USEPA-EGD, 29 February 1984.
2. Kohlmann Ruggerio Engineers, "1984 Alaskan Placer Mining
Study and Testing Summary Report," Preliminary Draft, September
Guidelines Division.
3. Shannon and Wilson, "Placer Mining Wastewater Treatment
Technology Project, Phase 2 Report," Prepared for the State of
Alaska Department of Environmental Conservation, November 1984.
4. Petterson, L. A.; Tsigonis, R. C.; Cronin, J. E.; and
Hanneman, K. L., "Investigation of the Effect of Total Suspended
Solids Levels on Gold Recovery in a Pilot Scale Sluice,"
September 1984.
5. Harty, D. M. and Terlecky, P. M., "Existing Wastewater
Recycle Practices at Alaskan Placer Gold Mines," Frontier
Technical Associates Memorandum to B. M. Jarrett, USEPA-EGD, 29
February 1984.
6. Harty, D. M. and Terlecky, P. M., "Geographic Distribution of
Mines Employing Partial or Total Recycle." Frontier Technical
Associates Memorandum to B. M. Jarrett, USEPA-EGD, 2 March 1984.
7. Dames and Moore, "Water Quality Data at Selected Active
Placer Mines in Alaska," Report No. 9149-001-22, September 17,
1976, prepared for Calspan Corporation.
VIII-54
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8. USEPA National Enforcement Investigations Center,
"Evaluation of Settleable Solids Removal Alaska Gold Placer
Mines," EPA Report No. 330/2-77-021, September, 1977.
9. Bainbridge, K. L., "Evaluation of Wastewater Treatment
Practices Employed at Alaskan Gold Placer Mining Operations,"
Report No. 6332-M-2, Calspan Corporation, Buffalo, N.Y., July
17, 1979.
10. R&M Consultants, Inc., "Placer Mining Wastewater Settling
Pond Demonstration Project," Prepared for the Alaska Department
of Environmental Conservation, June, 1982.
11. Harty, D. M. and Terlecky, P. M., "Reconnaissance Sampling
and Settling Column Test Results at Alaskan Placer Gold Mines,"
Frontier Technical Associates Report No. FTA-84-140211, November
15, 1983, Prepared for USEPA Effluent Guidelines Division.
12. Kohlmann Ruggiero Engineers, "Treatability Testing of Placer
Gold Mine Sluice Waters in Alaska, U.S.," Prepared for USEPA
Effluent Guidelines Division, January 1984.
13. Kohlmann Ruggiero Engineers, P. C., 1984 Alaskan Placer
Mining Study and Testing Report (Draft).
VIII-55
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SECTION IX
COST, ENERGY, AND OTHER NON-WATER QUALITY ISSUES
DEVELOPMENT OF COST DATA BASE
General
Generalized capital and annual costs for wastewater treatment
processes at placer mining facilities are based on cubic yards
of paydirt processed. Assumptions regarding the costs, cost
factors, and methods used to derive the capital and annual costs
are documented in this section. All costs are expressed in 1984
dollars (Engineering News Record, Construction Cost Index (CCI)
= 4161; third quarter of 1984).
The cost estimates were based on assumptions regarding system
loading and hydraulics, treatment process design criteria, and
material, equipment, personnel, and energy costs. These
assumptions are documented in detail in this section. The
estimates prepared have an accuracy of plus or minus 30 percent.
Fourth quarter 1984 vendor quotations were obtained for all major
equipment and packaged systems. Construction costs were based on
standard cost manual figures (see References IX-1 and IX-2)
adjusted to the fourth quarter, 1984.
The wastewater treatment unit processes studied are as follows:
Primary Settling
Secondary Settling
Flocculant (Polyelectrolyte) Addition
Recycle
IX-1
-------
The unit processes were used in five treatment options (See
Section VIII) as follows:
1. Primary settling with a six-hour detention time.
2. Primary settling, with a one-hour detention time, followed
by secondary settling with a six-hour detention time.
3. Primary settling, with a one-hour detention time, followed
by 80 percent recycle of the primary pond effluent to the
sluice and secondary settling of the remaining 20 percent
for six hours.
Primary settling, with a one-hour detention time, followed
by 80 percent recycle of the primary pond effluent to the
sluice and flocculant addition prior to secondary settling,
with a six-hour detention time of the remaining 20 percent
of the flow.
5. Primary settling, with a six-hour detention time, and
recycle of 100 percent of the treated water to the sluice.
It should be noted that, due to the limitations of this cost
estimating approach, the cost for equipment necessary to recycle
50 percent of the flow or more is basically the same. Therefore,
the cost for options using 80 or 100 percent recycle can be used
to estimate the cost of recycle of another percentage of 50
percent or more.
The above five options are shown schematically in Figures IX-1
through IX-3.
IX-2
-------
FIGURE IX-1. PLACER MINING - HASTEWATER TREATMENT OPTIONS
COSTING STUDY
INFLUENT
INFLUENT
PRIMARY
SETTLING
OPTION 1
PRIMARY
SETTLING
DISCHARGE
SECONDARY
SETTLING
OPTION 2
DISCHARGE
IX-2a
-------
FIGURE IX*2. PLACER MINING - HASTEWATER TREATMENT
COSTING STUDY
INFLUENT
REUSE
PRIMARY
SETTLING
SECONDARY
SETTLING
PUMPING 80% RECYCLE
DISCHARGE
OPTION 3
INFLUENT
REUSE
-4
PRIMARY
SETTLING
FLOCCULANT
ADDITION
SECONDARY
SETTLING
PUMPING 80% RECYCLE
DISCHARGE
OPTION 4
IX-2b
-------
FIGURE 1X-3. PLACER MINING - HASTEWATER TREATMENT OPTIONS
COSTING STUDY
INFLUENT
REUSE
PRIMARY
SETTLING
PUMPING
100* RECYCLE
OPTION
IX-2o
-------
CAPITAL COST
Capital Cost of Facilities
Figure IX-4 presents a schematic representation of a generic
placer mine treatment system. This diagram shows the distances
assumed between the various facilities which were used to
determine the materials required for the systems and the costs of
those materials.
Settling Ponds.
Construction costs for settling ponds were based upon assumptions
(specifically documented later in this section) regarding the
retention time and geometry of the ponds. Costs for earth moving
were based on a cost per cubic yard of material moved. The cost
of earth moving was determined by contacting Caterpillar Tractor
Co. and determining the earth-moving capacity of a new piece of
equipment. The capacities and costs supplied by the
manufacturer, are as follows:
Equipment Operating Capacity Lease Cost*
D-6 100 yd3/hr $ 71.44/hr
D-7 200 yd3/hr $ 90.37/hr
D-8 300 yd/hr $114.74/hr
D-9 500 yd/hr $182.45/hr
*Includes equipment, insurance, fuel and nominal maintenance.
Fuel cost was $1.75 gallon (Source: Lease Agency in Anchorage;
costs applicable to Fairbanks area).
(These estimates also reflect maneuvering time.)
IX-3
-------
IX-3a
-------
The estimated costs and hours to construct the settling ponds
were determined using a new machine. A sludge density (settled
solids) of 50 percent was used to calculate pond volumes needed.
Piping.
Capital costs for piping, were calculated for aluminum pipe, were
obtained from various suppliers and from References 1 and 2. The
costs include the cost of the pipe, delivery to the site, and
installation. Piping was sized based on normal velocities and
pressure drops used in engineering design. A minimum velocity of
2 1/2 feet per second was used.
Pumps.
Capital costs for horizontal centrifugal pumps with diesel engine
drives were otained from vendor telephone quotations and from
References 1 and 2. Installation and delivery costs were added.
The costs include piping and valves at the pump location.
Polyelectrolyte Feed Systems.
The capital costs for polyelectrolyte feed systems were obtained
from vendor telephone quotations; an installation and delivery
cost was added. The cost of a small electrical generator to
supply power to the polyelectrolyte feed system was also added.
Capital Cost of_ Land
Land costs were not included in the estimates since the
facilities would be constructed on land which is part of the
IX-4
-------
mining claims. Therefore, no additional costs would be incurred
for the land needed for the treatment facilities.
Capital Cost of_ Contingencies
Unless otherwise stated, a contingency cost of 20 percent was
added to the total capital costs generated to cover taxes,
insurance, over-runs, and other contingencies.
Deliveries and Installation Costs
All equipment costs were increased by 60 percent to account for
delivery and installation at remote regions in Alaska. The 60
percent factor for Alaska was suggested by a contact with Dodge
Reports.
ANNUAL COST
Annual Cost of Amortization
Initial capital costs were amortized on the basis of a 15 percent
annual interest rate with assumed life expectancy of 5 years for
general civil, structural, mechanical, and electrical equipment.
However, since the settling ponds will be constructed yearly,
their cost is written off every year.
n
(r) (1-Hr)
CRP=
n
d+r) -1
where CRF = capital recovery factor
r = annual interest rate - 15 percent, and
n = useful life in years - 5 years.
IX-5
-------
Therefore, CRF = 0.29832.
Annual cost of amortization was computed as:
Ca = B (CRF)
where Ca = annual amortization cost, and
B = initial capital cost.
Annual Cost of Operation and Maintenance
Maintenance.
Annual maintenance costs were assumed to be three percent of the
total mechanical and electrical capital cost (unless otherwise
noted) which excludes the annual costs of the ponds.
Reagents.
The following prices were used to estimate annual costs of
chemicals:
Polyelectrolyte $2.50/lb delivered
A dosage of 2 mg/1 was assumed in calculating the annual cost for
chemicals. This assumption is based on the settling tests
performed during the 1983 and 1984 treatability studies.
Annual Cost of_ Energy
The energy cost required for wastewater treatment is the cost of
fuel to drive the required engines. Fuel cost at $1.75 per
gallon, which includes delivery, was used to estimate costs.
IX-6
-------
(SOTTIOQ NI)
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IX-6a
-------
Facilities were assumed to operate 10 hours per day, 65 days per
year for mines smaller than 700 yd3/day, 75 days per year for
mines 700 to 1250 yd3/day, and 85 days per year for large
mines over 1250 yd^/day where we had no actual operating data
available. Figure IX-5 is a plot of flow rate versus cost per
hundred hours per year of operation.
TREATMENT PROCESS COSTS
Primary Settling
Capital Costs
The required sizes of primary settling ponds were determined by
hydraulic loading and design data obtained during field settling
tests. Primary settling ponds were sized for each option based
on one-hour and six-hour detention times. All pond volumes
include volume for flow including 20 percent for freeboard and
volume for sediment storage. In all cases/ the depth of ponds was
assumed as 12 feet, it was also assumed that a new pond would be
built when the water depth above the sediment reached a minimum
of 3 feet. A sediment density of 50 percent was used for design
purposes.
The wastewater was assumed to flow to and from the ponds by
gravity. In all options having primary and secondary ponds, it
was assumed the four primary ponds would be constructed each
mining season at different locations and that the spent ponds
would not be refilled. For the two options that have only
primary ponds, it was assumed that one pond would be constructed
IX-7
-------
each mining season. Figure IX-6 is a plot of flow rate versus
pond excavation volumes. Figure IX-7 is a plot of flow rate
versus time of excavation, and Figure IX-8 is a plot of flow rate
versus pond excavation cost. The curves are calculated using a
D-8 at the capacity and cost as presented above based upon 65
days of sluicing time.
Ponds having a three-hour detention time were also costed since
this detention time would produce an effluent close to that of a
six-hour detention pond. As can be seen from Figure IX-8, the
difference in cost for the six-hour and three-hour ponds is very
small and is within the cost-estimating accuracy. Therefore, the
six-hour settling ponds were utilized when preparing the cost
estimates.
Annual Costs.
Since the ponds will only be constructed for one mining season,
the annual amortized cost was assumed to be the construction cost
for each pond.
Secondary Settling
Capital Costs.
The required sizes of secondary settling ponds were determined by
hydraulic loadings and data obtained during field settling tests.
Secondary settling ponds were sized for six hours of detention
time based on 100 percent and 20 percent of the total flow. The
20 percent values reflect the amount of water that would be
discharged under the 80 percent recycle options.
IX-8
-------
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All pond volumes allow for a safety factor and sediment storage.
In all cases, the water depth was assumed to be 12 feet plus 20
percent of flow volume for freeboard, which includes the volume
require for sludge storage.
The wastewater was assumed to flow to and from the ponds by
gravity. One secondary pond would be constructed during the
mining season. Figure IX-9 is a plot of flow rate versus the
required volume of excavation for the secondary ponds. The cost
of excavation for secondary ponds are presented in Figures IX-7.
Annual Costs.
Since the ponds will only be constructed for one mining season,
the annual amortized cost was assumed to be the total
construction cost for each pond.
Piping
Capital Costs.
Piping is required after the primary pond whether or not a
secondary pond is used. Figure IX-4 shows a typical layout of a
placer mine treatment system with the assumed pipe lengths shown.
The length of pipe from one end of the primary pond to the other
will depend upon the flow rate which dictates the pond size.
IX-9
-------
IX-9a
-------
In addition, if recycle is practiced, piping will be required
from the recycle pumps to the sluice. This length of pipe is
also dependent on the flow rate and, in turn, the primary pond
size.
Prices for aluminum piping were obtained from manufacturers and
60 percent was added for transportation to the site and
installation. The pipe costs per thousand feet for various
diameters would be as follows:
4" - $2,900
6" - $5,400
8" - $8,500
10" - $10,700
12" - $13,200
The piping required at a mining site is for discharge piping and
recycle piping. A 500 foot length of pipe was utilized for
discharge for all mines costed. The length of recycle piping
depends upon the length of pond which is dictated by flow rate.
To the length of pipe required by pond sizing, a distance of 300
feet was added for the distance between the pond and sluice. The
cost for piping at various flows is presented in Figure IX-10.
Annual Costs.
Annual costs for piping systems were assumed to include the
following: (1) amortization calculated at 15 percent annual
interest over 5 years for equipment (CRP = 0.29832), and (2)
annual maintenance at 3 percent of total capital costs.
IX-10
-------
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IX-10a
-------
Flocculant Addition
Capital Costs.
Capital costs were estimated for flocculation systems consisting
of a metering pump mounted on a drum of diluted polyelectrolyte.
A single-sized system was used for all mine sites which includes
the flocculant supply system and generator to run the system.
This system has an installed cost of $3,000. A flocculant dosage
of 2 parts per million was used.
Local electrical and piping connections were included in the cost
estimates.
Annual Costs.
Amortization of capital cost for flocculation systems assumed a
15 percent annual interest rate with life expectancies of five
years for construcion (CRF = 0.29832). Additional costs were
estimated as follows: annual maintenance was assumed to be three
percent of capital cost; chemicals were costed at $2.50 per pound
for polymer. The cost of chemicals per 100 hours of operation
versus flow rates is plotted on Figure IX-11. This figure
indicates the cost for several chemical dosages.
Recycle
Capital Costs.
Cost estimates were prepared for installation of systems to
provide for 80 and 100 percent recycle of wastewater. Recycle is
IX-11
-------
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IX-lla
-------
accomplished by pumping the primary pond effluent wastewater back
to the sluicing operations for reuse. Any quantity greater than
the recycle rate would overflow the primary pond and flow to a
secondary pond. In preparing the cost estimates/ 50 percent
recycle was also costed. Due to the accuracy of the cost
estimating, the difference in cost for the equipment to recycle
50 percent or more of the flow is minimal; therefore, the costing
for 80 or 100 percent recycle can be utilized for any recycle
percentage above 50.
Recycle pumps are horizontal, centrifugal-type pumps complete
with diesel engines. The pumps are normally supplied as a
package which includes the pump, engine, and drive and are skid-
mounted. The estimated cost includes pump piping and valves.
Pumping equipment costs were based on vendor quotations. Local
piping, valves, and fittings were costed based on vendor
definitions and costing methodology in Reference 1.
Pumping equipment selection was based on hydraulic flow
requirements assuming a 75 foot total dynamic head requirement.
Total capital cost estimates include pumps, diesel engine
drivers, piping, valves, fittings, installation, and engineering
and contingencies (at 20 percent). Capital cost expressed as a
function of hydraulic flow rate is plotted in Figure IX-12.
Annual Costs.
Annual costs for wastewater recycle systems were assumed to
IX-12
-------
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include the following: (1) amortization calculated at 15 percent
annual interest over 5 years for equipment (CRF = 0.29832), (2)
annual maintenance at 3 percent of total capital costs, and (3)
fuel computed at $1.75 per gallon.
Construction Time
Due to the relatively short operating period per year available
at many sites, time required to construct the wastewater
treatment facilities can reduce the total available time for
mining. Therefore, estimates were also prepared on the time
required to construct and install the various facilities.
Pond Construction.
The hours required to construct the ponds were based on equipment
(D-6, D-7, D-8, and D-9 as appropriate) with variable capacities.
This capacity was determined by contacting the equipment
manufacturer.
Movement of_ Recirculation Pump.
Field observations indicate a three-hour period is needed to move
a recycle pump from one location to another.
Pipelines.
A seven-hour period was estimated to adjust the pipeline to a new
primary pond location.
IX-13
-------
Example of Cost Estimating for Placer Mine Site
The following is the method that can be utilized to determine the
estimated cost for the treatment at a mine site using the Figures
presented in this section. It should be noted that the cost
estimates prepared for mine sites presented later in this section
utilized actual calculations and not the Figures. For the
purpose of this example Model Mine number 4 was utilized. This
model has a sluice flow of 6,000 gpm and considers that the
sluice is operated 850 hours per year handling 153,000 cubic
yards of pay dirt.
Option _!
The option consists of a single settling pond (primary) with a
six-hour detention time and discharge piping of 500 feet.
Cost Estimate:
A. Capital Cost
Primary Pond - From Figure IX-7 $27,000
Piping - Discharge - From Figure IX-10 15,500
Total Capital Cost $42,500
B. Annual Operating Cost
Primary Pond Construction $27,000
Amortization of Piping (15,500 x .29832) 4,623
O & M for Piping (15,500 x .03) 465
Total Annual Cost $32,088
C. Hours to Construct (12 hrs/day)
IX-14
-------
Pond Construction - Using D-9 500 cy/hr 168 hrs
Installation of Piping 20 hrs
Total Hours 188
Total Man-Days 15.7
D. Cost per Cubic Yard Mined (32,088 + 153,000) $0.21
Option 2:
This option consists of a primary settling pond for one-hour
detention, followed by a secondary settling pond having a six-
hour detention time and discharge piping of 500 feet. The
primary pond will be constructed four times in a mining season.
Cost Estimate:
A. Capital Cost
Primary Pond - From Figure IX-7 $19,500
Secondary Pond - From Figure IX-7 11,000
Piping - Discharge - From Figure IX-10 15,500
Total Capital Cost $42,500
B. Annual Operating Cost
Primary Pond Construction $19,500
Secondary Pond Construction 11,000
Amortization of Piping (15,500 x .29832) 4,623
0 & M for Piping (15,500 x .03 465
Total Annual Cost $35,588
C. Hours to Construct (12 hrs/day)
Primary Pond - Using D-9 500 cy/hr 124 hrs
IX-15
-------
Secondary Pond - Using D-9 500 cy/hr 78 hrs
Installation of Piping 20 hrs
Total Hours 222
Total Man-Days 18.5
D. Cost per Cubic Yard Mined (35,588 + 153,000)
Option 3_
This option consists of a primary settling pond having one-hour
detention time followed by 80 percent recycle and secondary
settling of the remaining 20 percent of the flow. The system
requires a recycle pump, recycle piping and 500 feet of discharge
pipe. The option considers the construction of the primary pond
four times during the mining season.
Cost Estimate:
A. Capital Cost
Primary Pond - From Figure IX-7 $19,500
Secondary Pond - From Figure IX-7 2,500
Piping - Discharge - From Figure IX-10 4,000
Piping - Recycle - From Figure IX-10 22,000
Recycle Pumps - 80% Flow -
From Figure IX-12 36,000
Total Capital Cost $85,000
IX-16
-------
B. Annual Operating
Primary Pond Construction $19,000
Secondary Pond Construction 2,500
Power Cost - From Figure IX-5
(80% of Flow) 17,000
Amortization of Equipment
(62,000 X .29832) 18,500
O&M for Equipment 1,860
(62,000 x .03)
Total Annual Cost $59,360
C. Hours to Construct (12 hrs/day)
Primary Pond - Using D-2 500 cy/hr 124 hrs
Secondary Pond - Using D-9 500 cy/hr 61 hrs
Equipment Installation (Pipe and Pumps) 70 hrs
Total Hours 255
Total Man-Days 21.3
D. Cost per Cubic Yard Mined
(59,360 - 153,000) $0.39
Option 4_
This option consists of a primary settling pond having on
detention time which is constructed four times during the season.
Eighty percent of the effluent from the primary pond recycled to
use on the sluice and the remaining twenty percent of the flow is
treated in a secondary pond having a detention time of six hours
before discharge. Polyelectrolyte is added to the water entering
the secondary pond. This option requires recycle pumps, recycle
IX-17
-------
piping and 500 ft of discharge pipe.
Cost Estimate
A. Capital Cost
Primary Pond - From Figure IX-7 $19,500
Secondary Pond - From Figure IX-7 3,500
Piping - Discharge - From Figure IX-10 4,000
Piping - Recycle - From Figure IX-10 22,000
Recycle Pumps - 80% Flow -
From Figure IX-12 36,000
Polyelectrolyte System 3,000
Total Capital Cost $88,000
B. Annual Operating Cost
Primary Pond Construction $19,500
Secondary Pond Construction 3,500
Power Cost - From Figure IX-5
(80% of Flow) 17,000
Polyelectrolyte at 2 mg/1 - From
Figure IX-11 (20% of Flow) 2,000
Amortization of Equipment (65,000 x .29832) 19,390
0 & M for Equipment (65,000 x .03) 1,950
Total Annual Cost $63,340
IX-18
-------
C. Hours to Construct (12 hrs/day)
Primary Pond - Using D-9 500 cy/hr 124 hrs
Secondary Pond - Using D-9 500 cy/hr 61 hrs
Equipment Installation (Pipe, Pump, etc.) 74 hrs
Total Hours 259
Total Man-Days 21.6
D. Cost per Cubic Yard Mined (63,340 + 153,000) $0.41
Option 5_
This option consists of a single primary settling pond with a
six-hour detention time followed by recycle of 100% of process
water. The system requires pond, recycle pumps and recycle
piping.
Cost Estimate
A. Capital Cost
Primary Pond - From Figure IX-7 $27,000
Piping - Recycle - From Figure IX-10 38,000
Recycle Pump - From Figure IX-12 39,000
Total Capital Cost $104,000
IX-19
-------
B. Annual Operating Cost
Primary Pond Construction $27,000
Power Cost - From Figure IX-5 19,550
Amortization of Equipment (77,000 x .29832) 22,970
O&M for Equipment (77,000 x .03) 2,310
Total Annual Cost $71,830
C. Hours to Construct (12 hr/day)
Primary Pond - Using D-9 500 cy/hr 168 hrs
Equipment Installation (Piping and Pump) 59 hrs
Total Hours 227
Total Man-Days 18.7
D. Cost per Cubic Yard Mined (71,830 + 153,000) $0.47
Treatment Costs for Various Options for the Placer Mining
Industry
Table IX 1 projects the construction days required, annual costs,
and cost per cubic yard mined for 10 mines. The costs were
computed using actual data on construction days obtained at the
mines if actual data were available. The following is a list of
mines costed using data obtained at the mine for sluicing time,
yardage mined and flow. The data for solids concentrations were
also obtained at the mine site during treatability testing at the
mines listed below.
4169 4248
IX-20
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4173 4249
4180 4250
4244 4251
4247 4252
Table IX-2 presents a summary of the cost estimates showing
maximum, minimum, and average cost for annual operation and cubic
yards mined.
To determine the effect on the water treatment system including a
classification step for a mine that is not presently
classifying, mine number 4252 was used. For this mine, it was
assumed that a classification system would include a grizzly and
a double deck vibrating screen. The water flow after the
installation of a classification system at mine 4252 was assumed
to be 2000 gallons per cubic yard sluiced.
This flow is based on data from mines using classification
systems obtained during the 1983 and 1984 field studies and
discussions with personnel knowledgeable in the placer mining
industry. The cost estimates for this mine with and without the
classification system are presented on Table IX-1 (page 2). A
comparison of the two costs indicates a reduced operating cost
for wastewater treatment when a classification system is added to
the mining equipment because of a reduction in the amount of
water necessary to sluice a given amount of ore.
IX-21
-------
TABLE IX-2
U.S. ENVIRONMENTAL PROTECTION AGENCY
INDUSTRIAL TECHNOLOGY DIVISION
ENERGY AND MINING BRANCH
ALASKAN PLACER MINING INDUSTRY
WASTEWATER TREATMENT COSTS
0
1
ANNUAL COSTS
Maximum (*1000) 156
Minimum (*1000) 5
Average <*1000) 26.3
COSTS/CU.YD.
Maximum 1.05
Minimum 0.04
Average 0.31
P T I 0 N S
2345
160 185 207 229
5 16 17 17
27.6 42.5 46.6 50.3
1.23 2.54 2.74 2.82
0.05 0.11 0.12 0.12
0.35 O.71 O.7B 0.60
IX-21a
-------
Table IX-3 projects the construction days required, annual costs,
and cost per cubic yard mined for 4 model mines. The models,
classification, cubic yards sluiced per hour, and days of
operation assumed are as follows:
Model Mine Size yd3/hr sluiced Days Operating
1 Extra small 25 65
2 Small 50 65
3 Medium 100 75
4 Large 180 85
The costs were computed utilizing the above data and assuming 10
hours per day for operation and a water use rate of 2,000
gallons per cubic yard sluiced. Table IX-4 presents a summary
of the model mines cost estimates showing maximum, minimum, and
average cost for annual operation and cubic yards mined.
Cost estimates were not prepared for placer mining operations
which use dredges. There is basically no cost associated with
pollution control systems since most dredging operations approach
zero discharge of process wastewater from the recovery process by
the nature of the mining method (See Section III).
IX-22
-------
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IX-22a
-------
TABLE IX-4
U.S. ENVIRONMENTAL PROTECTION AGENCY
INDUSTRIAL TECHNOLOGY DIVISION
ENERGY AND MINING BRANCH
ALASKAN PLACER MINING INDUSTRY
WASTEWATER TREATMENT COSTS - MODEL MINES
0
1
ANNUAL COSTS
Maximum (tlOOO) 32
Minimum <*1000) 8
Average (*1000> 17.0
COSTS /CU. YD.
Maximum 0.49
Minimum O.21
Average 0.31
P T I 0 N S
2345
36 59 63 72
9 18 20 20
19.0 33.8 36 39.8
0.55 1.12 1.22 1.24
0.23 0.39 0.37 O.47
0.35 0.67 0.71 0.76
IX-22b
-------
REFERENCES
1. Means Construction Data - 1984, 42nd Annual Edition.
2. USEPA Municipal Environmental Research Laboratory,
"Estimating Water Treatment Costs," EPA-600/2-79-162.
3. Kohlmann Ruggiero Engineers, P.C., "Treatability Testing
of Placer Gold Mine Sluice Waters in Alaska, U.S.,"
Prepared for EPA Industrial Technology Division, January
1985.
4. Kohlmann Ruggiero Engineers, P.C., "1984 Alaskan Placer
Mining Study and Testing Report", Proposed for EPA
Industrial Technology Division, Washington, D.C., January
31, 1985.
5. Caterpillar Tractor Co., "Caterpillar Performance Handbook,
1984," revised edition.
IX-23
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SECTION X
BEST PRACTICABLE TECHNOLOGY (BPT)
This section identifies the effluent characteristics attainable
through the application of the best practicable control
technology currently available (BPT). See Section 301(b)(l)(A)
of the Clean Water Act. BPT reflects the existing performance by
plants of various sizes, ages, and processes within the gold
placer mining industry. Particular consideration is given to the
treatment already in place.
BPT limitations for eleven subcategories of the ore mining
industry were promulgated in 1978 and were upheld in the courts.
See Kennecott Copper Corp. v. EPA, 612 F.2d 1232 (10th Cir.
1979). Effluent limitations for the gold placer mine industry
were reserved until additional information could be developed.
While it is now long after the 1977 date to comply with BPT under
the Clean Water Act, EPA is proposing BPT because current
treatment at most existing placer mines is inadequate to
establish a baseline for limitations, including BCT and BAT.
The factors considered in identifying BPT include: 1) the total
cost of applying the technology in relation to the effluent
reduction benefits to be achieved from such application; 2) the
size and age of equipment and facilities involved; 3) the
processes employed; (4) nonwater quality environmental impacts,
(including energy requirements), and (5) other factors the
Administrator considers appropriate. These factors are considered
below. The Act does not require or permit consideration of
X-l
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water quality problems attributable to particular point sources
or industries, or water quality improvements in particular water
bodies in setting technology-based effluent limitations
guidelines. Accordingly, water quality considerations are not
the basis for selecting the proposed BPT. See Weyerhaeuser
Company v. Costle, 590 F.2d 1011 (D.C. Cir. 1976).
In general, the BPT level represents the average of the best
existing performances of plants of various ages, sizes, processes
or other common characteristics. Where existing performance is
uniformly inadequate, BPT may be transferred from a different
subcategory or category. Limitations based on transfer
technology must be supported by a conclusion that the technology
is, indeed, transferable and a reasonable prediction that it will
be capable of achieving the prescribed effluent limitations See
Tanners' Council of America v. Train, 540 F. 2d 1188 (4th Cir.
1976). BPT focuses on end-of-pipe treatment rather than process
changes or internal controls, except where such are common
industry practice.
The Agency studied the gold placer mining industry to identify
the processes used and the wastewaters generated by mining and
beneficiation.
As discussed in Section VIII, the control and treatment
technologies available to gold placer mines include both in-
process and end-of-pipe technologies. Based on the pollutants
found in the wastewater discharge, described in Section VI, and
the pollutants selected for control, See Section VII, the
X-2
-------
following three technologies were considered as possible bases
for BPT.
1. Simple Settling - Settling ponds are installed as a
single large pond but are often used in a multiple arrangement of
two or more ponds in series. Simple settling removes solids
found in wastewater and the ponds in series further reduce
settleable solids1 and total suspended solids (TSS)2
loadings in each of the sequential ponds. The principal involved
is to retain the wastewater long enough to allow the solids
(particulates) to settle while keeping the velocity of the flow
to a minimum approaching quiescent settling conditions. Sludge
storage is critical and must be considered in the design and
construction of a pond.
1Settleable solids is the particulate material which will
settle in one hour expressed in militers per liter (ml/1) as
determined using an Imhoff cone and the method described for
Settleable Solids in 209E Standard Methods for Examination of_
Water and Wastewater, 16th Edition.
^Total Suspended Solids (TSS) is the residue retained on a
standard glass-fiber filter after filtration of a well-mixed
water sample expressed in milligrams per liter (mg/1) using the
method described for Total Suspended Solids Dried at 103"-
105° in 209C Standard Methods for Examination of Water and
Wastewater, 16th Edition.
X-3
-------
Virtually all commercial gold placer mines operating in 1984 and
1985 had settling ponds of varying numbers, sizes, and
efficiencies. The effluent limitations contained in NPDES
permits for placer mines were based on the use of settling ponds;
as a result, the technology is available and in use by the
industry. However/ sampling data and other information on
existing ponds indicate that most ponds are inadequately
designed, constructed, or maintained to consistantly produce an
acceptable effluent quality or concentration of solids
(settleable solids and TSS). In Section IX of this document,
treatment facilities to control solids with simple settling
technology are designed and costed to provide 6 hours of settling
in well designed, constructed, and operated settling ponds which
reduce the flow velocity to a minimum and have sufficient volume
for sludge to preclude remixing or cutting of solids from the
sludge back into the effluent. (The reasons for selecting a 6-
hour settling period are discussed below). As discussed in
Section VI and Table VI-1, the long term achievable levels for
solids based on 1984 data from existing treatment at placer mines
is less than 0.2 ml/1 settleable solids and less than 2000 mg/1
TSS. Field treatability tests indicate settleable solids are
reduced to less than 0.2 ml/1 with about 3 hours quiescent
settling as discussed in 1984 Alaskan Placer Mining Study and
Testing Report, January 31, 1985. A general engineering design
concept is that doubling quiescent settling time in settling
tests will provide a retention time in an actual pond with a
generous margin of reliability. Finally, Discharge Monitoring
X-4
-------
Reports (DMR) from mines which reported to Region X in 1984
revealed over 2600 individual grab samples with settleable solids
at 0.2 ml/1 or less.
2. Recycle of Process Wastewater - Recycle of process
wastewater from simple settling ponds is discussed in Section
VIII. As we discussed there, high rate recycle of over 50 percent
is practiced by commercial placer mines of all sizes, i.e.,
production capacity, and in all mining districts for which we
have data. Recyling only requires the addition of a pump at the
settling pond(s) and piping back to the gold recovery process.
In Section VIII, three different recycle options were considered:
80 percent recycle from primary settling followed by secondary
settling of the 20 percent blowdown, 80 percent recycle and
flocculant addition to the 20 percent blowdown, and 100 percent
recycle from primary settling. Less than 80 percent recycle was
not considered because while the reduction in the mass of
pollutants is a direct function of the percent recycle, the cost
of recycle of 80 percent or more is approximately the same as the
cost of 50 percent recycle. Flocculant addition and the
attainable limitations using flocculants are discussed below.
The attainable effluent limitations for discharge of blowdown
from an 80 percent recycle system are the same as for simple
settling, 0.2 ml/1 settleable solids and 2000 mg/1 TSS, but the
mass of pollutants discharged is 80% less than the mass of
pollutants from once-through simple settling. The effluent
limitation based on 100 percent recycle is no discharge of
X-5
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process wastewater.
3. Coagulation and Flocculation
The use of flocculants is also discussed in Section VIII.
Coagulation and flocculation is not used by existing gold placer
mines, but is used in wastewater treatment facilities in many
industrial categories, by many mines and mills in other
subcategories of the ore industry, and by coal mines and coal
preparation plants. Flocculant addition and coagulation
increases the size of particles for settling by forming floes of
individual particles that act as a simple particle which settle
faster because of the increased weight and size over the
individual particles. Pilot testing of the use of flocculants
was conducted at placer mines which indicate that attainable
effluent limitations for coagulation and flocculation are zero
settleable solids and less than 100 mg/1 TSS.
Specialized Definitions for Gold Placer Mines:
The proposed effluent limitations guidelines are for facilities
discharging wastewater from mines that produce gold or gold
bearing ones from gold placer deposits and the beneficiation
processes to recover gold or gold bearing ore which use gravity
separation methods. The proposal does not apply to gold mines
extracting ores (hard rock ores and mines) other than placer
deposits nor to the gold ore mills associated with hard rock
mines regardless of the extraction process used in the mills.
The proposal does not apply to the wastewater from gold or gold
ore extraction processes from gold placer deposits that use
X-6
-------
cyanide or other chemicals for leaching gold or to extraction
processes that use froth flotation methods. These effluents are
regulated in the 1982 rulemaking for ore mining.
The data and information contained in this document apply
primarily to the p_roce_ss_ wastewater discharges from the
beneficiation process. The proposed effluent limitations
guidelines limit this process wastewater. However, other
wastewater such as mine drainage and groundwater infiltration is
often commingled with the process wastewater. The effluent
discharge of the commingled wastewater is also limited as
discussed in "Specialized Provisions for Gold Placer Mines,"
below.
Because the considerations for defining effluent limitations and
standards for gold placer mines differ from other industries,
including the rest of the ore mining category in 40 CFR 440, EPA
is proposing definitions which would apply only to gold placer
mines. All other definitions in the general regulations (40 CFR
Part 401) and the ore mining regulation (40 CFR Part 440) apply.
(1) Gold placer deposit means an ore consisting of metallic
gold-bearing gravels, which may be: residual, from weathering of
rocks in-situ; river gravels in active streams; river gravels in
abandoned and often buried channels; alluvial fans; sea-beaches;
and sea-beaches now elevated and inland.
(2) Gravity separation methods means the treatment of
mineral particles which exploits differences between their
X-7
-------
specific gravities. The separation is usually performed by means
of sluices, jigs, classifiers, spirals, hydrocyclones, and
shaking tables.
(3) Process wastewater means all water used, in and
resulting from the beneficiation process, including but not
limited to, the water used to move the pay dirt or ore to and
through the beneficiation process, the water used to aid in
classification or screening, the water used in the gravity
separation methods, and the precipitation on and runoff from the
beneficiation process area.
(4) Beneficiation process means the dressing or processing
of ores for the purpose of (i) regulating the size of the ore or
product, i.e., classification or screening; (ii) removing
unwanted constituents of the ore, and (iii) improving the
quality, purity, assay grade of a desired product, i.e., by
gravity separation methods.
(5) Beneficiation process area means the combined areas of
land used to stockpile pay dirt or ore immediately before the
beneficiation process, stockpile the tailings immediately after
the beneficiation process, including the area of land (i.e.,
drainage below the sluice) from the stockpiled tailings to the
treatment system, and the area of the treatment system, e.g.,
holding pond(s) or settling pond(s).
(6) Groundwater infiltration means that water which enters
the treatment facility as a result of the interception of natural
springs, aquifers, and other seepage or run-off which percolates
X-8
-------
into the ground and seeps into the treatment facility's pond or
wastewater holding facility.
The effluent limitations guidelines and standards for all ore
mine and dressing facilities are applicable to point sources
discharges from active mines and active mills and beneficiation,
and not applicable to closed, or abandoned mines and mills, or
discharges from mine areas being reclaimed, or point or non point
sources from areas outside of the mine area. Specific
definitions for ore mining and dressing promulgated in 40 CFR 440
which are pertinent to gold placer mines are discussed below.
(1) Mine is an active mining area, including all land and
property placed under, or above the surface of such land, used in
or resulting from the work of extracting metal ore or minerals
from their natural deposits by any means or method, including
secondary recovery of metal ore from refuse or other storage
piles, wastes, or rock dumps and mill tailings derived from the
mining, cleaning, or concentration of metal ores.
(2) Active mining area is a place where activity related to
the extraction, removal, or recovery of metal ore is being
conducted, except, with respect to surface mines, any area of
land on or in which grading has been completed to return the
earth to desired contour and reclamation work has begun.
(3) Mine drainage means any water drained, pumped, or
siphoned from a mine.
Summary of Proposed BPT Effluent Limitations Guidelines
X-9
-------
As discussed in Section IV, for the purpose of developing
effluent limitations guidelines and standards, gold placer mining
is defined as a separate subcategory in the Ore mining and
dressing point source category. The gold placer mining
subcategory is broken down further according to the size of the
facility (capacity to process ore) and type of mining process.
The basis for breakdown by size is the potential economic impact
to small commercial mines and large commercial mines.
As discussed in Section IV, the proposal does not cover mines
that process less than 20 cubic yards of ore per day
(yd3/day), or to dredges which operate in open water, e.g.,
open marine waters, bays, or major rivers. At the present time,
EPA does not believe such limitations are warranted. These small
mines are generally intermittent, "non-commercial" operations.
The Agency believes that because of the diversity among these
operations and the nature and volume of their discharge compared
to "commercial mines," the preferable approach is to develop
effluent limitations and standards for these facilities in the
permit process based on the permit writer's best professional
judgment. The dredges in open waters are not covered because the
Agency has no information as to number, location, or applicable
technologies for these facilities. Permits for these operations
would likewise be based on the permit writer's best professional
judgment.
The rest of the gold placer mine industry has been subcategorized
into three groups:
X-10
-------
1. All mines using all mining methods with a beneficiation
process capacity of 20 to 500 yd3/day.
2. All mines using all mining methods with a beneficiation
process capacity of over 500 yd^/day (except large dredges
with capacity of over 4000 yd3/day).
3. Large Dredges which process more than 4000 yd3/day.
Proposed BPT effluent limitations for the first two groups i.e.,
all mining methods with beneficiation capacity of over 20
ydvday except large dredges, are based on simple settling
technology (option 1) with limitations on settleable solids and
TSS. While many mines with capacities of 20 to 500 yd3/day
were identified in the economic analysis document as possible
base line closures, or potentially not profitable before any
costs of water pollution control were imposed on the model mines,
simple settling is essentially the only end-of-pipe practicable
technology available for raw discharge. Raw discharge is not
consistent with the objective of the Act which is to restore and
maintain the chemical, physical, and biological integrity of the
Nation's waters. Ponds (simple settling) are presently the
standard practice of the industry because existing permits limits
are based on this technology. The limitations on settleable
solids and TSS can be attained at existing mines with careful to
construction and maintenance of settling facilities as discussed
in Section VIII. The size of the ponds to provide retention to
attain the limitations combined with the relief provision for
X-ll
-------
precipitation as discussed below, are reasonable. The
limitations for TSS are proposed as 2000 mg/1 monthly average/
based on a typical monitoring frequency for TSS of one sample per
month. In earlier development documents for ore mining and
dressing and in the preambles to regulations for the industry,
EPA identified settleable solids as the primary pollutant
regulated to control solids from placer mines because the
analysis is relatively easy to perform and unlike TSS does not
require storage and transit to a laboratory. On the other hand,
TSS analysis must be performed in a laboratory. EPA recognizes
it is often not feasible for remote placer mines to sample,
properly preserve the sample, and deliver the sample for TSS
analysis to a laboratory on a frequent basis. However, sampling
once every 30 days for TSS will generally require only 3 or 4
samples per mine per mining season. In light of the heavy solids
load in placer mining wastewater, EPA believes it is reasonable
to require regulation of TSS, and in turn monitoring for TSS, for
placer mines.
BPT limitations for large dredges (over 4000 yd3/day) is
proposed to be no discharge of process wastewater based on the
existing practice at these large dredges which requires high rate
recycle approaching 100 percent recycle as part of the mining
system. At least 3 operating dredges for which EPA has data are
not discharging process wastewater (100% recycle) within the
definitions and provisions discussed below. No discharge is
practicable and requires a minimum investment and modification to
processes at existing large dredges which are not already meeting
X-12
-------
the no discharge of process wastewater standard.
The cost/benefit inquiry for BPT is a limited balancing,
committed to EPA's discretion, which does not require the Agency
to quantify benefits in monetary terms. See, e.g., American Iron
and Steel Institute v. EPA, 526 F.2d 1027 (3rd Cir. 1975). In
balancing costs in relation to effluent reduction benefits, EPA
considers the volume and nature of existing discharges, the
volume and nature of discharges expected after application of
BPT, the general environmental effects of the pollutants, and the
cost and economic impacts of the required pollution control
level.
Raw wastewater from the beneficiation process at commercial size
placer mines (processing more than 20 yd3/day, all methods)
is described in Section VIII of this document and, based on 1984
data, averaged 50 ml/1 settleable solids and 30,000 mg/1 TSS.
The beneficiation processes at these mines produce over 16,000
million pounds per year of water born solids (TSS) in the
extraction process. As discussed in the technical memorandum
"Placer Mining Industry Contaminants Removed by Wastewater
Treatment", Kohlmann Ruggiero Engineers, November 1984,
implementation of limitations on solids at the proposed BPT
levels would reduce solids by over 93 percent as compared to the
untreated effluent. The cost of this reduction as determined
from the model costs in Section IX of this document is $6.9
million/year assuming no treatment facilities are presently in
place (or new construction must replace treatment facilities).
The pollutant removed is solids (settleable solids and TSS); the
X-13
-------
effect of solids on the environment is discussed in Section VII
of this document. The economic impact on the industry is
discussed in detail in the Economic Analysis of Proposed Effluent
Limitations and Standards for the Gold Placer Mining Industry.
EPA believes the benefit of the proposed BPT effluent limitations
justify the cost of implementation.
EPA has considered the nonwater quality environmental impact
(including energy requirements) of the proposed BPT effluent
limitations. EPA believes the proposed BPT regulation best
serves competing national goals where the elimination or
reduction of one form of pollution may aggravate other
environmental problems. The implementation of treatment to meet
BPT effluent limitations will not create any additional air
pollution emissions. Considering the solid waste generation of
the mining and beneficiation of gold placer deposits where often
5 to 6 tons of overburden (solid waste) is removed to mine one
ton of paydirt, where beneficiation to recover the gold often
leaves over 98% of the ore as solid waste or tailings, the solid
waste generation or the sludge left by BPT is inappreciable.
Imposition of the proposed BPT and the settling ponds to obtain
the limitations will require some land area for the ponds, but
the land will normally be available in the area left from mining.
BPT will require a small increase in energy consumption to
provide fuel for the construction or mining equipment used to
build and maintain t&e ponds and other earthen structures for
wastewater treatment. Gravity flow is normally used to convey the
process wastewater to and through treatment and discharge;
X-14
-------
therefore no energy is required for pumping at commercial mines
except large dredges. Large dredges require pumps as part of
their mining and beneficiation process and no additional pumps
are required.
The proposed BPT limitations are summarized below.
Best Practicable Technology (BPT) for Gold Placer Mines
Subcategory
Effluent
Characteristics
Effluent
Limitations
Instantaneous Monthly
Maximum Average
Settleable Solids 0.2
TSS
2000 mg/1
Settleable Solids 0.2 ml/1
TSS
2000 mg/1
Mines with
beneficiation
capacity of 20 to
500 yd3/day of
paydirt (all mining
methods)
Mines with
beneficiation
capacity of over
500 yd3/day
of paydirt (all
mining methods
except large dredges
with capacity of over
4000 yd3/day)
Large Dredges with
beneficiation
capacity of over
4000 yd3/day
of paydirt
Specialized Provisions for Gold Placer Mines
The 1982 regulation for the ore mining and dressing industry has
specialized provisions for combined (commingled) waste streams,
as well as a storm exemption. The proposed regulation for gold
placer mines includes similar provisions, with certain changes
necessary to accommodate the particular considerations for gold
placer mining. The following provisions are proposed for gold
No Discharge of Process Wastewater
X-15
-------
placer mines.
(1) Combined Waste Streams; Where process wastewater is
commingled with mine drainage or groundwater infiltration, this
combined waste stream may be discharged if the concentration of
each pollutant or pollutant property does not exceed the effluent
limitations applicable to mines processing 20 to 500 yd^/day.
However, the volume of commingled wastewater that may be
discharged does not include the flow or volume of process
wastewater where the effluent limitation for the berieficiation
process is no discharge of process wastewater.
(2) Storm Exemption for Facilities Not Subject to Effluent
Limitations Guidelines and Standards Requiring No Discharge of_
Process Wastewater; If, as a result of precipitation (rainfall or
snowmelt), a source with an allowable discharge has an overflow
or excess discharge of effluent which exceeds the limitations or
standards, the source may qualify for an exemption from such
limitations and standards with respect to such discharge if the
following three conditions are met:
(i) The treatment system is designed, constructed, and
maintained to contain or treat the maximum volume of untreated
process wastewater which would be discharged by the beneficiation
process during a 6-hour operating period without an increase in
volume from precipitation or groundwater infiltration, plus the
maximum volume of runoff resulting from a 5-year, 6-hour
precipitation event. In computing the maximum volume of water
which would result from a 5-year, 6-hour precipitation event, the
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operator must include the volume which would result from all
areas contributing runoff to the individual treatment facility,
i.e., all runoff that is not diverted from the active mining area
and all runoff which is allowed to commingle with the influent to
the treatment system.
(ii) The operator takes all reasonable steps to maintain
treatment of the wastewater and minimize the amount of overflow.
(iii) The operator complies with the notification
requirements of the National Pollutant Discharge Elimination
System (NPDES) regulations contained in 40 CFR 122 8122.41 (m)
and (n). The storm exemption is designed to provide an
affirmative defense to an enforcement action. Therefore, the
operator has the burden of demonstrating to the appropriate
authority that the above conditions have been met.
(3) Storm Exemption for Facilities Subject to Effluent
Limitations Guidelines and Standards Requiring No Discharge of
Process Wastewater; If, as a result of precipitation (rainfall or
snowmelt), a source which is subject to effluent limitations
guidelines and standards requiring no discharge of process
wastewater has an overflow or discharge which violates the
limitations or standards, the source may quality for an exemption
from such limitations or standards with respect to such discharge
if the following conditions are met:
(i) The treatment system is designed, constructed, and
maintained to contain the maximum volume of process wastewater
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stored, contained, and used or recycled by the beneficiation
process during normal operating conditions without an increase in
volume from precipitation or groundwater infiltration plus the
maximum volume of wastewater resulting from a 5-year, 6-hour
precipitation event. In computing the maximum volume of
wastewater which would result from a 5-year, 6-hour precipitation
event, the operator must include the volume which would result
from all areas contributing runoff from the beneficiation process
area, i.e., all runoff that is not diverted from the treatment
system for the beneficiation process.
(ii) The operator takes all reasonable steps to minimize
the overflow or excess discharge.
(iii) The operator complies with the notification
requirements of the National Pollutant Discharge Elimination
System (NPDES) regulations contained in 40 CFR Part 122 8122.41
(m) and (n). The storm exemption is designed to provide an
affirmative defense to an enforcement action. Therefore, the
operator has the burden of demonstrating to the appropriate
authority that the above conditions have been met.
(4) Groundwater infiltration provision; In the event a
source which is subject to no discharge of process wastewater
effluent limitations guidelines and standards can demonstrate
that groundwater infiltration contributes an uncontrollable
amount of water to the treatment system's impoundment or
wastewater holding facility, the permitting authority may allow
the discharge of a volume of water equivalent to the amount of
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groundwater infiltration. This discharge shall not exceed the
effluent limitations applicable to a mines with beneficiation
capacity in the range of 20 yd3/day to 500 yd3 of pay
dirt or ore per day.
Guidance for Implementing the Specialized Provisions for Gold
Placer Mines
Following is guidance for implementation of the special
provisions above to assist permit writers who may include these
provisons in NPDES permits and mine operators who wish to design,
construct, and maintain their treatment facilities to quality for
these provisions.
Storm Exemption to Establish an Upset to the Treatment System
1. The exemption is available only if it is included in
the operator's permit. Many existing permits have exemptions or
relief clauses stating requirements other than those set forth
above. Such relief clauses remain binding unless and until this
proposed regulation is issued as a final regulations and the
storm exemption is incorporated into the operator's permit.
2. The storm provision is an affirmative defense to an
enforcement action. Therefore, if this provision appears in the
final regulation, there is no need for the permitting authority
to evaluate each settling pond or treatment facility permitted at
that time.
3. Relief can be granted to ore process wastewater
discharges and combined waste streams.
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4. The relief only applies to the increase in flow caused
by precipitation on the facility and surface runoff.
5. Relief is granted as an exemption to the requirements
for normal operating conditions when there is an overflow,
increase in volume of discharge, or discharge from a by-pass
system caused by precipitation.
6. Relief can be granted for discharges during and
immediately after any precipitation or snowmelt. The intensity
of the event is not specified.
7. The provision does not grant, nor is it intended to
imply, the option of ceasing or reducing efforts to contain or
treat the runoff resulting from a precipitation event or
snowmelt, regardless of the intensity of the precipitation. The
operator must continue to operate the treatment facility to the
best of the operator's ability during and after any
precipitation.
8. Relief can be granted from all effluent limitations and
standards, i.e., in BPT, BAT, BCT, and NSPS.
9. In general, the relief is intended for discharges from
tailings ponds, settling ponds, holding basins, lagoons, etc.,
that are associated with and part of treatment facilities. The
relief will most often be based on the construction and
maintenance of these settling facilities to "contain" a volume of
water.
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10. The term "contain" for facilities which are allowed to
discharge must be considered in conjunction with the term "treat"
discussed in paragraph 11 below. The containment requirement is
intended to insure that the facility has sufficient capacity to
provide 6 hours of settling time for the volume resulting from a
5 year, 6 hour precipitation event. This is the settling time
required to "treat" influent so that it meets the daily effluent
limitations and standards. The theory is that a settling
facility with sufficient volume to contain the runoff from a 5-
year, 6-hour rainfall plus 6-hours discharge of normal process
wastewater and normal combined waste streams (e.g., without an
increase in volume from precipitation) can provide a minimum 6-
hour retention time for settling of the wastewaters even if the
pond is full at the time the storm occurs. The water entering
the pond as a result of the storm is assumed to follow a last-in,
last-out principle. Because of this, the "contain" and
"maintain" requirement for facilities which are allowed to
discharge does not require providing for draw down of the pool
level during dry periods. The volume can be determined from the
top of the stage of the highest dewatering device to the bottom
of the pond at the time of the precipitation event. There is no
requirement that relief be based on the facility being emptied of
wastewater prior to the rainfall or snowmelt upon which the
exemption is provided. The term "contain" for facilities which
are allowed to discharge means the wastewater facility's holding
pond or settling pond was designed to include the volume of water
that would result from a 5-year, 6-hour rainfall.
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11. The term "treat" applies to facilities which are
allowed to discharge and means the wastewater facility was
designed, constructed, and maintained to meet the daily maximum
effluent limitations for the maximum flow volume in a 6-hour
period. The operator has the option to "treat" the flow volume
of water that would result from a 5 year, 6 hour rainfall in
order to qualify for the storm water exemption. To compute the
maximum flow volume, the operator includes the maximum flow of
wastewater including mine drainage and groundwater infiltration
during normal operating conditions without an increase in volume
from precipitation plus the maximum flow that would result from a
5-year, 6-hour rainfall. The maximum flow from a 5-year, 6-hour
rainfall can be determined from the Water Shed Storm Hydrograph,
Penn State Urban Runoff Model, or similar models.
12. The term "treat" offers to the operator alternatives to
the simple settling provided by settling ponds upon which
effluent limitations are based. Examples of alternatives are:
1) clarifiers designed and operated to "treat" the maximum flow
volume, but which would not have the actual volume to provide an
actual 6-hour retention time; and 2) flocculants to aid settling
and, if properly used, allow a smaller settling pond to obtain
the same results as a larger settling pond, e.g., 6-hour
retention of the wastewater.
13. The term "maintain" is intended to be synonymous with
"operate." The facility must be operated at the time of the
precipitation event to contain or treat the specified volume of
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wastewater. Specifically, in making a determination of the
ability of a facility to contain a volume of wastewater or to
provide 6-hours of retention of wastewater to treat a volume or
flow, sediment and sludge must not be permitted to accumulate to
such an extent that the facility cannot hold the volume of
wastewater resulting from 6-hours of normal process wastewater
discharge and normal combined waste streams plus the volume
resulting from a 5-year, 6-hour rainfall. That is, sediment and
sludge must be removed as required to maintain the specific
volume of wastewater required for the exemption, or the
embankment must be build up or graded to maintain a specific
volume of wastewater required, or a new settling pond must be
built and used.
14. The term "contain" for facilities treating only process
wastewater subject to no discharge means the wastewater facility
is designed, constructed, and maintained to hold, without a point
source discharge, the volume of water that would result from a 5-
year, 6- hour rainfall, in addition to the normal amount of water
which would be in the wastewater facility for recycle and reuse
to the beneficiation process, e.g., without an increase in volume
from precipitation. The operator treating only process
wastewater must provide for freeboard under normal operating
conditions equivalent to the volume that would result from a 5-
year, 6-hour rainfall on the beneficiation process area
(including the ponds).
15. The storm provision for no discharge of process
wastewater must be considered in conjunction with the combined
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waste stream provision which would allow a discharge from a
treatment system treating (1) process wastewater with a no
discharge limitation and (2) commingled mine drainage and ground
water infiltration. The volume allowed to be discharged would be
the volume attributable to the mine drainage and groundwater
infiltration. The storm provision for facilities treating these
combined waste streams would be based upon the sum of the
elements or volumes to: (1) "contain" the process wastewater
subject to no discharge and runoff from the beneficiation area as
discussed in 14 above to determine a volume, to which would be
added the volume required to (2) contain or treat the volume of
mine drainage and groundwater infiltration (combined waste
streams) allowed to be discharged as discussed in 1.0 and 11
above.
Mine Drainage from Active Mining Areas of Gold Placer Mines
1. "Active mine areas" include the excavations in mines;
refuse/ middling/ and tailings areas; tailings ponds, holding and
settling basins; and other areas ancillary to a mine. Active
mine areas do not include areas unaffected by mining or
beneficiation of pay dirt.
2. "Mine drainage" includes all water which contacts an
"active mining area" and which naturally flows into a "point
source" - a discernible, confined, and discrete convenience - or
is collected in, or channeled or diverted to a "point: source,"
i.e., settling ponds.
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3. Water which contacts an "active mining area" and either
does not flow, or is not channeled by the operator, to a point
source, is considered nonpoint source runoff, and the proposed
regulations do not require the mine operator to collect and treat
such runoff. The proposed regulations require the placer mine
operator to treat runoff which contacts an active mining area and
is discharged from, or collected in a point source, and is
commingled in a "combined waste stream."
4. When an existing mine is permanently closed, effluent
limitations and standards of performance for the ore mining and
dressing point source category, including placer mines, are no
longer directly applicable.
5. Mine drainage handling is a part of most methods and
systems used to mine or extract ore. At many ore mines, mine
drainage is handled and treated to meet specific effluent
limitations and standards for mine drainage both during the
periods the mine is actually working and also during idle periods
when the mine is not actually working, i.e., weekends, vacation
periods, strike periods, idle days, idle shifts, and temporary
closures of the mine. Mine drainage handling is often required
full-time to maintain the mine and treatment of this mine
drainage is also required full-time to meet effluent limitations
and standards for mine drainage discharges. This mine drainage
from a mine when it is not actually working is still considered
to be from an "active mining area." However, gold placer mines
differ from other metal mines and other hard rock gold mines in
that most gold placer mines are seasonal and operate only in the
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summer, or less than 4 months a year. Also, operating data on
gold placer mines indicate most placer mines operate one shift
per day for about 10 hours. Finally, specific limitations and
standards for mine drainage from gold placer mines are not
proposed, although limitations and standards for mine drainage
are included to the extent that mine drainage is commingled in
combined waste streams. Therefore, limitations and standards for
mine drainage, e.g., combined waste streams, are applicable only
when mine drainage is commingled with process wastewater.
Process wastewater is considered to be discharged from the time
the beneficiation process is started until the time the volume of
combined wastewater would be discharged, calculated on last in,
last out considerations, e.g., retention time in the settling
pond.
6. The proposed effluent limitations guidelines and
standards for gold placer mines are not applicable during the off
season. They are applicable from the time the beneficiation
process is first started in a calender year to the time the
beneficiation process is last loaded and used in a calender year,
e.g., the mining season.
7. While the proposed effluent limitations guidelines and
standards are applicable to process wastewater and combined waste
streams during the mining season, other "point source discharges"
during the mining season, i.e., segregated mine drainage and mine
camp runoff and sewage, may be subject to separate permit
limitations; as well as "point source discharges" before and
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after the mining season, i.e., mine drainage, construction runoff
and mine camp discharges. Limitations for these discharges would
be determined based on best professional judgement by the
permitting authority.
Guidance to Determine Process Capacity
1. The proposed effluent limitations guidelines and
standards are directly applicable to mines with a beneficiation
process with the capacity to process more than 20 yd3 of pay
dirt per day. In the course of developing effluent limitations
guidelines and standards for gold placer mines, EPA established
three groups in the gold placer mining subcategory: (1) all
mines with a beneficiation process with the capacity to process
more than 20 yd3 and less than 500 yd3 of pay dirt per
day; (2) all mines with a beneficiation process with a capacity
to process more than 500 yd3 of pay dirt per day, except
large dredges; and large dredges with a beneficiation process
with a capacity to process more than 4000 yd3 of pay dirt per
day.
2. The pay dirt processed is measured as "bank run" pay
dirt which is the volume of pay dirt as measured in place in its
natural state and before extraction or mining and before the
swell in volume that occurs when compacted material in place is
broken and stacked; i.e., in a stockpile.
3. Applications for NPDES permits are usually made and the
permits for a given mining season written before the start of the
mining season. Therefore, determinations as to permit conditions
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and whether effluent limitations guidelines and standards are
even applicable to a specific gold placer mine's discharge must
be made before the mining and processing that determine the
mine's size begins. A mine's size therefore must be determined
based on information supplied by the mine operator as part of the
permit application.
4. Many permits are a reissue of an existing permit to the
same mine operator who uses the same equipment as used previously
at essentially the same location to mine and process pay dirt.
For these permits which are reissued, the mine operator may use
data and information from the previous season or year to
determine the mine's size of 1 to 20 yd3/day, 20 to 500
yd^/day, over 500 yd^/day, and for dredges over 4000
ycP/day. However, should the status and operation of the
mine be scheduled for a change, i.e., from prospecting and
exploration to production status or from low production to a
higher production with additional equipment, the mine operator
must notify the permitting agency of this forecast or anticipated
increase in pay dirt mined and processed. The mine operator
would make an estimate of the amount of bank run pay dirt that
will be mined in the coming season as discussed below.
5. Many permit applications will be made by operators
planning to mine during the next season for the first time in an
area that was mined by a different operator the previous season,
by mine operators who are increasing production as mentioned in 4
above, and by mine operators who are opening new mines which are
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"new sources" or "new discharges" (as defined in the NPDES
regulations, 40 CFR Part 122). For these permits, the mine
operator must provide the best estimate of the mine's size, e.g.,
capacity to process pay dirt.
6. The capacity to process pay dirt used to determine a
mine's size (yd3/day) is based on the average amount of
paydirt moved through the benefication process (i.e., sluice) in
a calendar day (24-hour period) whether the working day is one or
more shifts. For reissue of an existing permit for an existing
mine as discussed in 4, the mine operator would divide the total
bank run material (yd^) mined in a year or season by the
number of days the beneficiation process was operated. EPA
believes most mines have records or logs of the amount of paydirt
processed in a season or can estimate the amount processed with
reasonable accuracy and similarly, have records or logs of the
number of days per season the gold recovery process was operated.
Since permit conditions will be based on a mine's size when the
proposed regulations are promulgated, most mine operators will
have the opportunity to establish and keep records of pay dirt
processed and the number of days the mine processes the pay dirt.
7. For permit applications discussed in 5, estimates of
capacity to process pay dirt are also based on the average amount
of pay dirt moved through the benefication process in a calendar
day. While the permit applicant cannot base the application on
personal experience mining at the location, if the same or
similar equipment, i.e., handbook capacity, is used, then the
information from the previous operator can be used to determine
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the capacity in yd3/day. For mines that are increasing
production, going from prospecting or assessment to production,
or are new sources or new dischargers, EPA believes that most
miners make an assessment as to the viability of investing money
and time in the venture, at least to the extent of estimating how
much pay dirt they will process and how many days their sluice
will operate. These estimates are acceptable for the purpose of
determining the mine size.
8. EPA believes that only a very few gold placer mines
will be in a range of production where exactly 500 ydvday
capacity will be a critical issue. The vast majority of the
mines making application for permits will be obviously larger or
smaller than 500 ydvday. For example, based on data for
1984 permits, less than 9 percent of the applications were for
mines with capacities of 400 to 600 yd^/day. EPA believes
that this magnitude of production and range will continue for
mines. However, for those few mines where the production rate is
critical and the capacity of the beneficiation process approaches
very closely the 20 yd^/day or the 500 yd-'/day cutoff,
the permitting authority may request periodic or mid-season
reporting of paydirt processed and days the beneficiation process
was operated to determine the production rate, and issue or
change permit limitations accordingly.
9. At the end of the mining season or at the end of the
year when the final DMR is submitted, the operator should
indicate the actual capacity of the beneficiation process for
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that season or year.
10. EPA recognizes that the information and data submitted
by a mine operator on how much paydirt will be processed during a
season or calendar year are the mine operator's good faith
estimates based on the operators professional judgment and
experience in mining and operating gold placer mines or are based
on the judgment of a mining professional, i.e., mining consultant
or professional mining engineer, who is familar with the mine.
EPA does not believe that exactly 500 yd-*/day will be
critical for most mines as discussed in 8 above. However,
statements of estimates and reported production (ydvday)
must be made in good faith because the data will be used to
determine what group of mines (larger or smaller than 500
ydVday) the operation belongs in and what effluent
limitations and standards apply. The statements made in a NPDES
permit application are subject to Title 18, U.S.C. E 1001 which
states that "Whoever, in any matter within the jurisdiction of
any department or agency of the United States knowingly and
willfully falsifies, conceals or covers up by any trick, scheme,
or device a material fact, or makes any false, fictitious or
fraudulent statements or representations, or makes or uses any
false writing or document knowing the same to contain any false,
fictitious or fraudulent statement or entry, will be fined not
more than $10,000 or imprisoned not more than five years, or
both."
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SECTION XI
BEST CONVENTIONAL POLLUTANT CONTROL TECHNOLOGY (BCT)
Section 301(b)(2)(E) of the Act requires categories and classes
of point sources, other than publicly-owned treatment works, to
achieve effluent limitations that require the application of the
best conventional pollutant control technology (BCT) for control
of conventional pollutants as identified in Section 304(a)(4).
The pollutants that have been defined as conventional by the
Agency, at this time, are biochemical oxygen demand, suspended
solids, fecal coliform, oil and grease, and pH. BCT is not an
additional limitation; rather, it replaces BAT for the control of
conventional pollutants.
Section 304(b)(4)(B) of the Act requires that, in setting BCT,
EPA must consider: the age of equipment and facilities involved,
the process employed, the engineering aspects of the application
of various types of control techniques, process changes, non-
water quality environmental impacts (including energy
requirements), and other factors the Administrator deems
important. Candidate technologies must also pass a two-part test
of "cost reasonableness" as discussed below.
A. Candidate Technologies
As discussed in Section VIII, four treatment options were
considered for placer mines using three treatment technologies:
simple settling, recycle of process wastewater at 80 percent and
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100 percent, and coagulation and flocculation of the 20 percent
blowdown from 80 percent recycle. For the purpose of developing
effluent limitations, EPA considered each of these treatment
options in light of the Section 301(b)(4)(B) factors listed above
for each of the three segments of the gold placer mining
subcategory.
Wastewater pollutant levels and pollutant concentrations
achievable by each option were determined using the same
information and data discussed in Section X for achievable BPT
limitations. Recycle of 80 percent and 100 percent are add-on
technology to BPT which would require additional equipment
including pumps and piping to meet the more stringent
limitations. Flocculant addition is an add-on to the 80 percent
recycle option that would require still more additional equipment
and supplies such as mixers, metering devices, and the
flocculants themselves to further treat the 20 percent blowdown
from 80 percent recycle. In increasing order of cost to
implement, and pounds of solids removed, the options are: 80
percent recycle, 80 percent recycle with flocculant addition to
the 20 percent blowdown, and 100 percent recycle.
Of the three add-on options, 100 percent recycle obviously offers
the largest removal of pollutants. Also, as discussed below,
this technology would pass the two part "cost-reasonableness"
test for BCT for all mines with beneficiation capacity over 20
yd^/day (all mining methods, including dredges).
1. Gold Recovery with the 100 Percent Recycle Option
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A repeated concern of industry commenter's is that recycle of
wash water reduces gold recovery in a sluice because of the
higher concentrations of TSS found in recycled wastewater
compared to once-through wash water. However, no conclusive data
have been offered by the industry to quantify any loss or, if
there is a loss, what TSS concentration starts to effect a loss.
Lacking any hard and verifiable data from industry, EPA decided
to conduct its own tests to obtain data on the effect of recycle
on gold recovery. As discussed in Section VIII of this document,
EPA funded studies to ascertain if a loss of recoverable gold
occurred in a pilot-scale sluice when the TSS concentration in
the wash water was varied from almost zero to about 200,000 mg/1.
The results of the tests provide EPA the only hard and verifiable
data on the effect of TSS concentration on gold recovery.
These tests indicate that over 99 percent of the gold is
effectively recovered regardless of the TSS concentration in the
wash water, e.g., recycle does not affect the recovery of gold in
the size range of +100 mesh. The tests also indicate there may
be some migration of the recovered gold down the sluice to lower
riffles as the TSS concentration increases, but settling of the
recycle water for 6 hours would reduce the TSS concentration to
less than 2000 mg/1 and in turn, reduce any migration. EPA
therefore believes that 100 percent recycle of process wastewater
will not materially effect gold recovery in a sluice.
Based on the 1984 total production of the industry (yd^/day
of pay dirt processed), over 20 percent of the production is
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processed with wash water that is 90 percent to 100 percent
recycled as discussed in Section VIII. Also, recycle (generally
because of a shortage of water) is employed in most mining
districts for which we have information, indicating that pumping
and powering of the pumps is a viable process change, even in
remote locations.
2. Mines with Processing Capacity of 2£ to 500 yd^/Day
As discussed in Section IV of this document, the mines with
processing capacity of less than 500 yd3/day are identified
in the Economic Development Document as generally not viable
operations under the assumptions employed to estimate cost items
for water pollution control, operating and mining expenses, and
income from gold recovered. Therefore, the subcategory for mines
with beneficiation capacity of 20 to 500 yd^/day (all mining
methods except dredges) was established to address the economic
considerations. While 80 percent recycle, with and without
flocculant addition to the blowdown, are technologies that are
less costly than 100 percent recycle, implementation of these
technologies is economically unachievable for this segment of the
industry which is projected to be unprofitable in the baseline,
i.e., before any water pollution control costs were imposed.
Given the general implications of the economic analysis, EPA is
proposing no more stringent limitations for BCT than BPT
limitations for mines in this group. For the reasons discussed
in Section VII, EPA is regulating TSS at BCT. Based on the
technology selected for this group of mines, i.e., simple
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settling, the BCT limitation on TSS is 2000 mg/1 monthly average.
As with the BPT limitations for TSS, EPA is recommending that
NPDES permit monitoring requirements consist of one sample and
analysis per month which EPA believes is a reasonable requirement
for placer mines, considering their remote locations.
3t Mines with Processing Capacity o£ Over 500 yd3/Day
No discharge of process wastewater is proposed for mines with
beneficiation capacity of over 500 yd3/day of pay dirt (all
methods). A no discharge requirement passes the cost-
reasonableness test discussed below and is economically
achievable for large mines. Just as most mines with benefication
capacity of less than 500 yd3/day (all mining methods) are
projected to be unprofitable, most mines above this size are
projected to be financially healthy and capable of installing
additional treatment to simple settling upon which BPT was based,
including the pumps, piping, and ancillary equipment to obtain no
discharge of process wastewater through 100 percent recycle.
4. Large Dredges with Processing Capacity of_ Over 4000
yd3/Day
For large dredges (larger than 4000 yd3/day), EPA is
proposing BCT limitations equal to the BPT limitat'ions i.e., no
discharge of process wastewater. Therefore, there is no
incremental cost to go from BPT to BCT. EPA has identified no
more stringent technologies to control process wastewaters from
these large dredges and BCT can not be less stringent than BPT.
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B. BCT Cost T_esj:
In addition to other factors specified in Section 304(b)(4)(B),
EPA assesses BCT limitations in light of a two-part "cost-
reasonableness" test. The first test compares the cost for
private industry to reduce its conventional pollutants with the
costs to publicly owned treatment works for similar levels of
reduction in their discharge of these pollutants. The second
test examines the cost-effectiveness of additional industrial
treatment beyond BPT. EPA evaluates both tests as measures of
"reasonableness". In no case may BCT be less stringent than BPT.
EPA published its methodology for carrying out the BCT analysis
on August 29, 1979 (44 FR 50372). In American Paper Institute y_^
EPA, 660 F.2d 954 (4th Cir. 1981), the Court of Appeals ordered
EPA to correct data errors underlying EPA's calculation of the
first test, and to apply the second cost test. (EPA had argued
that a second cost test was not required). On October 29, 1982,
the Agency proposed a revised BCT methodology (47 FR 49176). EPA
also published a notice of data availability on September 20,
1984 (49 FR 37046).
The BCT cost reasonableness analysis for the placer Gold Mining
Industry is discussed in the study entitled "Cost Effectiveness
Analysis of Proposed EFfluent Limitations and Standards for the
Placer Gold Mining Industry" which is included in the record of
the rulemaking. In this report, EPA first evaluated the cost per
pound of solids (TSS) removed incrementally by each treatment
option above the previous option for a sample of 10
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representative placer mines. Annual treatment costs for each
option in addition to the cost per pound of solids removal were
estimated using data obtained at the 10 mine sites during
treatability tests performed in 1984 (See Section VII and "1984
Alaskan Placer Mining Study and Testing Report," Kohlmann
Ruggiero Engineers, January 1985). EPA also analyzed the cost
per "pound equivalent" (i.e.; pounds of toxic pollutants weighted
by a measure of their toxicity) removed at the 10 mines. The
results presented in the report indicate all of the options
considered were extremely "cost-effective" in terms of their
removal efficiency for toxic pollutants and total solids.
For the purpose of performing the aforementioned BCT cost-
reasonableness tests however, EPA calculated estimates of the
aggregate or industry-wide cost of solids removed by the
recommended BPT and BCT options. To arrive at these overall cost
per pound figures, EPA utilized the model mine framework
developed for its analysis of the economic impacts of this
regulation (See Economic Impact Analysis, EPA 440/02-85-026,
August 1985). The cost per pound incurred by the entire industry
at BPT is approximately $0.00062, while the cost for large mines
only (i.e.; those processing 500 cubic yards of material per day
or more) is $0.00058. Small commercial mines (i.e.; those
processing between 20-500 cubic yards per day) would incur an
aggregate cost per pound of approximately $0.00061 at BPT. At
the more stringent technology (100% recycle of process
wastewater) recommended for BCT, the cost per pound of solids
removed beyond BPT is $0.002 for large mines. The cost at BCT
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for small mines is also in this range, but no more stringent
technology beyond BPT is recommended for these mines since it is
believed that many are unprofitable under current economic
conditions.
EPA considers the above cost figures to be one cent per pound
removed since the actual estimated values are reasonable by any
interpretation and because no smaller unit of currency exists;
i.e., there is no other meaningful denomination. Therefore, when
rounded to a cost, both of the BCT cost-reasonableness tests are
"passed," and the candidate technology for BCT for both large and
small mines is cost reasonable. See the aforementioned cost-
effectiveness study for further details.
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C. Summary of Proposed BCT Limitations
The proposed BCT limitations are summarized below:
Best Conventional Pollutant Control Technology
Subcategory
Mines With
Beneficiation Capacity of
20 to 500 yd3/day of Paydirt
(all Mining Methods)
Mines With
Beneficiation Capacity of
over 500 yd3/clay of Paydirt
(all Mining Methods Except Dredges
with beneficiation capacity of over
4000 yd3/day of paydirt)
Large Dredges With
Beneficiation Capacity of
over 4000 yd3/day of Paydirt
Effluent Limitation
TSS - 2000 mg/1
Monthly Average
No discharge of
Process Wastewater
No Discharge of
Process Wastewater
Specialized Definitions and Provision
The specialized definitions, commingled wastestream provisions/
and storm exemption discussed in Section X for BPT are also
proposed to be applicable to BCT.
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SECTION XII
BEST AVAILABLE TECHNOLOGY ECONOMICALLY ACHIEVABLE (BAT)
This section identifies effluent limitations based on best
available technology economically achievable (BAT). See Section
301{b)(2)(A) of the Clean Water Act. These limitations are based
on the best control and treatment technology employed by a
sepecific point source within the point source category or
subcategory, or by another industry where it is readily
transferable. Emphasis is placed on additional treatment
techniques applied at the end of the treatment systems currently
employed for BPT, as well as improvements in process control and
treatment technology optimization.
Input to BAT selection includes all materials discussed and
referenced in this document. As discussed in Section VII, ten
sampling and analysis programs were conducted to evaluate the
presence/absence of toxic pollutants. A series of pilot-scale
treatability studies was performed at several locations within
the industry to evaluate BAT alternative.
Consideration was also given to:
1. Age and size of facilities and equipment involdved
2. Process(es employed
3. In-process control and process changes
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4. Cost of achieving the effluent reduction by application
of the alternative control or treatment technologies
5. Nonwater quality environmental impacts (including
energy requirements)
In general, the BAT technology level represents the best
economically achievable performance of plants of various agesf
sizes, processes, or other shared characteristics. Those
categories whose existing performance is uniformly inadequate may
require a transfer of BAT from a different category. BAT may
include feasible process changes or internal controls, even when
not in common industry practice.
This level of technology also considers those plant processes and
control and treatment technologies which at pilot-plant and other
levels have demonstrated both technological performance and
economic viability at a level sufficient to justify
investigation.
The Agency has reviewed a variety of technology options and
evaluated the available possiblities to ensure that the most
effective and beneficial technologies were used as the basis of
BAT. EPA examined technology alternatives which could be applied
to placer mining BAT options and which would represent
substantial progress toward prevention of environmental pollution
above and beyond progress achievable by BPT.
The Clean Water Act requires consideration of costs in BAT
selection, but does not require a balancing of costs against
effluent reduction benefits (see Weyerhaeuser v. Costie, 11 ERG
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2129 (DC Cir. 1978)). In developing the proposed BAT, however,
EPA has given substantial weight to the reasonableness of costs
and reduction of discharged pollutants. The Agency has
considered the volume and nature of discharge before and after
application of BAT alternatives, the general environmental
effects of the pollutants, and the costs and economic impacts of
the required pollution control levels. The options presented
represent a range of costs so as to assure that affordable
alternatives remain after the economic analysis. The rationale
for the Agency's selection of BAT effluent limitations is
summarized below.
EPA considered the same treatment and control options discussed
in Section VIII which were considered for BPT as the technology
options for BAT: simple settling, recycle of process wastewater
at 80 percent, recycle of process wastewater at 100 percent, and
coagulation and flocculation of the 20 percent blowdown from 80
percent recycle. For each of the subcategories set out in
Section IV, EPA reviewed the various BAT factors listed above to
determine whether different BAT effluent limitations guidelines
for certain groups of gold placer mines might be appropriate.
As discussed in Section VIII, although the regulation for gold
placer mines is not being issue under a schedule established in
the NRDC Settlement Agreement, EPA has decided to apply the
criteria for regulating (or in the alternative excluding from
regulation) toxic pollutants and subcategories established in
Paragraph 8 of the Decree. Data collected by EPA from individual
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mines within the industry were used in deciding which specific
toxic pollutants would be regulated.
Paragraph 8(a)(iii) of the Settlement Agreement allows the
Administrator to exclude from regulation toxic pollutants not
detectable by analytical methods developed under Section 304(h)
of the Clean Water Act or other stat-of-the-art methods. This
provision also applies to pollutants below EPA's nominal
detection limit. In addition, Paragraph 8(a)(ii) allows the
exclusion of pollutants that were detected in amounts too small
to be effectively reduced by technologies known to the
Administrator. One hundred and nine toxic organics, cyanide and
eleven toxic metals are excluded from regulation under these
provisions.
Paragraph 8(a) (iii) also allows the Administrator to exclude
from regulation pollutants detected in the effluent of only a
small number of sources within the category and uniquely related
to those sources. The toxic organic pollitant methylene chloride
was detected in the effluent at three mines during the screen
sampling program and Bis(2-Ethylhexyl)Phthalate was found at one
mine. These two organics are attributed to sample and laboratory
contamination. Methylene chloride and Bis(2-Ethylhexyl)Phthalate
are therefore excluded under this provision.
Paragraph 8(a) (iii) of the Settlement Agreement also allows the
Administrator to exclude from regulation pollutants that are
effectively controlled by the technology upon which other
effluent limitations guidelines and standards are based. As
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described more fully in Section VII and Section XI, EPA has
determined that solids, primarily the solids put into suspension
by the benefication process at placer mines, are the principal
pollutant in the wastewater from placer mines and, furthermore,
that limiting the discharge of solids controls other pollutants
which are found in the solid form. Therefore, the Agency is
basing limitations more stringent than BPT on the control of
solids: TSS, a conventional pollutant controlled under BCT, and
settleable solids, a non-conventional pollutant controlled under
BAT. The Agency believes that arsenic and mercury found in
discharges from placer mines are adequately controlled by the
incidental removal associated with the control and removal of
settleable solids and TSS found in the discharges. If TSS are
controlled to meet the BCT limitations, and settleable solids are
controlled to meet the BAT limitations, any arsenic and mercury
in the discharge would be reduced to levels that would be
proposed if arsenic and mercury were controlled directly e.g.,
the concentrations promulgated to control arsenic and mercury in
the ore mining and dressing point source category regulation.
See 40 CFR Part 440.
The 1982 final effluent limitations guidelines and standards for
ore mining and dressing excluded the toxic pollutant asbestos
from direct effluent limitations because effluent limitations on
solids (TSS) effectively controlled the discharge of asbestos
(chrysotile). Asbestos was found in all raw waste discharges and
all effluent from all ore mines and mills where an analysis was
made for asbestos (88 samples representing 23 mine/mill
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facilities). EPA found a high degree of correlation between
solids and chrysotile asbestos in the raw wastewater and treated
wastewater and concluded that settling tehnology was so
successful at removing solids, an effluent limitation on asbestos
was not appropriate inlight of the correlation with solids and
the expense of monitoring specifically for asbestos. The Agency
believes that efflunet limitations on solids in the discharge
from gold placer mines would also control the discharge of
asbestos.
Turbidity has been the subject of some controversy as to what
achievable levels can be obtained by various treatment
technologies and what levels of turbidity are acceptable water
quality for various uses. Turbidity is not a toxic pollutant;
rather, turbidity is a nonconventional pollutant which can be
controlled by direct BAT limitations on the levels of turbidity
that may be discharged or by indirect control through limitations
on other pollutant parameters, i.e., solids. As discussed in
Section VII, turbidity is a measure of the light scattering
properties of water. Turbidity levels are a function of and the
result of suspended solids in water; the mass, size, shape, and
refractive index of the solids in the water affect the measured
turbidity. Since turbidity is a function of solids levels, EPA
is proposing BAT effluent limitations on settleable solids, a
nonconventional pollutant.
For each of the gold placer mining subcategories, the Agency has
not identified any technology more stringent than those proposed
here for BAT which are attainable and economically achievable
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within the Act. The Act does not permit consideration of water
quality problems attributable to a point source or industry or
water quality improvements in particular water bodies in setting
technology-based effluent limitations guidelines. Water quality
considerations are not and can not be the basis for selecting
BAT. See Weyerhauser Company v. Costle, 590 F. 2d 1011 (D.C.
Cir. 1976). Effluent limitations on turbidity may be included in
NPDES permits if necessary to meet state water quality standards.
For large dredges and mines with beneficiation process capacity
larger than 500 yd3/day (all mining methods), EPA is
proposing no discharge of process wastewater based on total
recycle of process wastewater as the BAT effluent limitation
guideline. These effluent limitations are the same as the BCT
effluent limitations. EPA is not proposing any more stringent
limitations because we have not identified any more stringent
technologies to control process wastewater pollutants from these
groups of gold placer mines.
For mines with beneficiation process capacity of 20 to 500
ydvday (all mining methods) EPA is proposing BAT effluent
limitations on settleable solids (SS) based on simple settling
technology equal to BPT and BCT limitations on SS. EPA is not
proposing BAT effluent limitations guidelines for these smaller
mines based on partial (80 percent) or total (100 percent)
recycle because, as discussed in Section IX and in the Economic
Impact Analysis, effluent limitations based on these technologies
would not be economically achievable for this group of mines.
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EPA is not proposing BAT effluent limitations based on
coagulation and flocculation of the blowdown from partial
recycle because technical questions remain to be resolved
regarding the use of flocculants on the wastewater discharges
from gold placer mines (as discussed in Section VIII) and the
economic impact on these smaller mines of partial recycle is not
economically achievable.
The proposed BAT effluent limitations are summarized below:
Best Available Technology Economically Achievable
Subcategory Effluent Limitations
Mines with Benefication Settleable Solids - 0.2 ml/1
Capacity of 20 to 500 yd3/day Instantaneous Maximum
of Paydirt (all mining methods)
Mines with Benefication No Discharge of Process
Capacity of over 500 yd3/day Wastewater
of Paydirt, (all mining methods
except Large Dredges with capacity
of over 4000 yd3/day of paydirt)
Large Dredges with Benefication No Discharge of Process
Capacity of over 4000 yd3/day Wastewater
of Paydirt
Specialized Definitions and Provisions
The specialized definitions, provisions for commingled waste
streams and the storm exemption discussed in Section X for are
also applicable to BAT effluent limitations guidelines.
Engineering Aspects of Best Available Technology Economically
Achievable
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The implementation of technology to attain BAT effluent
limitations will not create any additional air pollution
emissions. The amount of solid waste generated by the technology
for BAT limitations is negligible compared to the amount
generated by mining and processing. Land requirements for
settling ponds at mines processing less than 500 yd3/day (all
methods) and at large dredges are no more than the requirements
for BPT. For mines processing more than 500 yd^/day (all
methods except large dredges), there is a small increase in
anticipated land requirements. However, land already mined will
generally be available.
Recycling of process wastewater may have a short-term impact on
water use downstream from the mine on a stream with limited flow.
However, this short-term impact will most often be negligible
because once the amount necessary for recycling is removed, the
remaining flow, as well as subsequent flow, will continue
downstream. In addition, flow will be higher quality, i.e., it
will not contain pollutants from placer mining. It is not
intended that mines upstream deny water to downstream users
impounding excess water above the amount used in the process or
allowed by their water right.
Recycle of process wastewater at mines with a benefication
process capacity of over 500 yd3/day will create in increase
in energy consumption for power to drive recycle pumps. At many
mines, gravity flow is used to bring water to the benefication
process and these mines will require the addition of a pump and a
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means to drive the pump. Most mines do not have electricity
available for such pumps and EPA believes the mines will probably
purchase a form of skidmounted diesel or gasoline direct drive
engine/pump. In determining the cost to implement the no
discharge of process wastewater requirement by recycle/ EPA
included the cost to purchase a skid-mounted unit and the fuel to
run the unit. However, in actual practice/ EPA has observed that
many mines are already using pumps to supply wash water either
one time through or recycled process wastewater. These mines
with pumps to supply wash water will have little if any increase
in energy consumption to recycle 100 percent of the process
wastewater.
There will also be an increase in energy consumption to provide
power for the equipment to build and maintain the wastewater
treatment facilities (settling and holding ponds). However, in
determining the cost to implement the technology for sample
settling or recycle, EPA used the value of the equipment and
labor time of the equipment already at the mine and the equipment
operators already at the mine. The equipment time for building
and maintaining ponds is a small part of the total equipment
hours available in a mining season; the energy consumption to
build and maintain ponds is negigible compared to the total
energy requirement for mining in a season. For example, the mine
represented by Model B in Section IX would use about 225
machine/operator days to mine and process in a season and about
15 machine/operator days to build and maintain a 100 percent
process wastewater recycle facility.
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The largest Impact on mines processing more than 20 ydvday
(all mining methods except large dredges) is the cost to meet the
design, construction, and operation requirements of a proper
treatment system, e.g., to meet the requirements of the storm
exemption, consisting of settling ponds for mines processing less
than 500 yd^/day and holding ponds for recycle of process
wastewater for mines processing more than 500 yd^/day. The
construction and operation of facilities that will quality for
the strom exemption is discussed in Section X. Most mines for
which EPA has data and information on existing ponds will have to
construct and maintain larger ponds with better construction and
design than are presently being used. Attention to detail will
be required to address such factors as: surface areas of the
pond, rate of flow through the pond, eliminating short circuiting
of flow across the pond, and entrace and exit effects of the
effluent. A number of handbooks are available to assist the mine
operator in the design, construction, and maintainance of ponds,
including "Placer Mining Settling Pond Design Handbook," January
1983, States of Alaska Department of Environmental Conservation.
The use of the concepts depicted in such handbooks will greatly
facilitate the mine operator complying in with the BAT effluent
limitations.
As discussed above, the Clean Water Act does not require a
balancing of costs against effluent reduction benefits. However,
included in the record supporting the proposed regulation, is the
Agency's report "Cost Effectiveness Analysis of Proposed EFfluent
Limitations for the Placer Gold Mining Industry" which calculates
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two measures of effectiveness of the proposed regulation: pounds
of TSS removed as discussed in Section XI and pounds of priority
(toxic) pollutants removed weighted by an estimate of their
toxicity/ e.g., pound-equivalents removed. Non-regulated
pollutants, i.e., arsenic and mercury, are included when they are
removed incidently as a result of a particular treatment
technology. The cost-effectiveness in terms of pound equivalent
removed for sample mines with beneficiation capacity of over 500
yd^/day (all mining methods except large dredges) which is
the group of placer mines with BAT more stringent than BPT is
acceptable and justifies the approximate $212 per pound
equivalent removed. In addition for all estimated mines in this
group, the cost per pound of solids removed in BPT to BAT is less
than $0.002 or over a million tons of solids at a cost of about
$3,300,000.
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SECTION XIII
NEW SOURCE PERFORMANCE STANDARDS (NSPS)
The basis for new source performance standards (NSPS) under
Section 306 of the Act is best available demonstrated technology.
New facilities have the opportunity to implement the best and
most efficient ore mining and milling processes and wastewater
technologies. Congress, therefore, directed EPA to consider the
best demonstreated process changes and end-of-pipe treatment
technologies capable of reducing pollution to the maximum extent
feasible.
EPA proposed that new source gold placer mines achieve new source
performance standards that are equivalent to the effluent
limitations guidelines proposed for BCT and BAT. The general
wastewater characteristics costs to treat and percentage of
pollutant removals from new sources are expected to be similar to
existing sources.
These performance standards would apply to process wastewater as
defined in the specialized definition discussed in Section X.
The combined (commingled) waste stream provision and storm
exemption which apply to BPT and BAT also apply to NSPS. See
Section X.
EPA is unable to identify any more stringent limitations for
mines with beneficiation capacity of over 500 yd-*/day than
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the no discharge requirement. For beneficiation processes of
less than 500 yd3/day, EPA is not proposing any more
stringent limitations for new sources than what is required for
existing sources. EPA expects that the financial condition of
new source mines smaller than 500 yd3/day will be similar to
existing mines of this size and that more stringent standards may
prevent new people from entering the placer mining industry,
i.e., it may pose a barrier to entry. Since the new source
standards are equivalent to the existing source standards, these
proposed NSPS will not pose a barrier to entry.
New Source Performance Standards
Subcategory Effluent Limitation
Mines With Beneficiation Settleable Solids - 0.2 ml/1
Capacity of 20 to 500 yd3/day Instantaneous Maximum
of Paydirt (all mining methods) TSS - 2000 mg/1
Monthly Average
Mines With Beneficiation Capacity No Discharge of
of over 500 yd3/day of Paydirt Process Wastewater
(all mining methods except Large
Dredges with Capacity of over
4000 yd3/day of paydirt)
Large Dredges With No Discharge of
Beneficiation Capacity of Process Wastewater
over 4000 yd3/day of
Paydirt
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SECTION XIV
PRETREATMENT STANDARDS
Section 307(b) of the Act requires EPA to promulgate pretreatment
standards for both existing sources (PSES) and new sources (NSPS)
of pollution which discharge their wastes into publicly owned
treatment works (POTWs). These pretreatment standards are
designed to prevent the discharge of pollutants which pass
through, interfere with, or are otherwise incompatible with the
operation of POTWs. In addition, these standards must require
pretreatment of pollutants, such as certain metals, that limit
POTW sludge management alternatives. The legislative history of
the Act indicates that pretreatment standards are to be
technology-based and, with respect to toxic pollutants, analogous
to BAT.
EPA did not propose pretreatment standards for existing sources
(PSES) or new sources (PSNS) in the ore mining and dressing point
source category in the 1982 rulemaking nor is it proposing such
standards for the gold placer mine subcategory since there are no
known or anticipated discharges to publicly owned treatment works
(POTWs).
•frU.8. GOVERNMENT PRINTING OFFICE 1985 491 191 46106
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