United States            Office of Water
          Environmental Protection Agency   (4303)
December 2011
V>EPA   Method 1627: Kinetic Test Method
           for the Prediction of Mine Drainage
           Quality
          December 2011

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  U.S. Environmental Protection Agency
            Office of Water
    Office of Science and Technology
Engineering and Analysis Division (4303T)
    1200 Pennsylvania Avenue, NW
        Washington,  DC 20460
          EPA-821-R-09-002

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                                      Background

Method 1627 was validated in an interlaboratory study involving laboratories from the federal, state,
commercial, mining industry, and academic sectors. The method was peer reviewed by experts from the
Minnesota Department of Natural Resources, U.S. Bureau of Land Management, U.S. Department of
Energy, Pennsylvania State University, and the Western Research Institute. Other than the dedication
below and minor formatting changes, the text of this document is the same as the May 2009 version of the
method.

                                  Acknowledgments

Support for the development of Method 1627 was provided by personnel in the U.S. Department of
Interior's Office of Surface Mining, the Pennsylvania Department of Environmental Protection, and the
Computer Sciences Corporation.  Data or other contributions were  made by Mahaffey Laboratory, Ltd.,
Geochemical Testing, Pennsylvania State University, the U.S. Geological Survey, Benchmark Analytical,
Consol Energy, ProChem Analytical, Sturm Environmental Services, and West Virginia University.

                                       Dedication

This method is dedicated to the memory of Roger Hornberger, without whom the method and supporting
data would not be available. Mr.  Hornberger spent most of his life in the Schuylkill Haven area of
Pennsylvania, earning a BS in landscape architecture and an MS in geology from Penn State University.
He joined the Pennsylvania Department of Environmental Protection in 1978, and became the District
Mining Manager in Pottsville, in  1987.

His extensive concern and expertise regarding coal mining, particularly in the Eastern United States, has
significantly benefited both the mining industry and the environment. His interest in overburden analysis
as a tool that could be applied to predict post-mining water quality  began in the early 1980s. The
analytical procedures described in this method, and its extensive amount of supporting data, are one of
many fruits of Mr. Hornberger's dedication and passion to filling this need. The individuals who knew
and worked with Roger are forever appreciative of his enthusiasm,  professionalism, extreme expertise,
and unique ability to assemble and facilitate teams of experts across multiple agencies, organizations, and
disciplines.

                                       Disclaimer

Mention of trade names or commercial products does not constitute endorsement or recommendation for
use.
                                        Contacts

Lemuel Walker
U.S. EPA
Engineering & Analytical Support Branch
Engineering and Analysis Division
Office of Science and Technology, Office of Water
1200 Pennsylvania Avenue NW (4303T)
Washington, DC 20460
OSTCWAMethods@epa.gov
EPA Method 1627                                 i                                   December 2011

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                                   Table of Contents
                                                                                         Page
1.0    Scope and Application	1
2.0    Method Summary	1
3.0    Limitations / Interferences	2
4.0    Safety	3
5.0    Apparatus and Materials	3
6.0    Reagents	6
7.0    Sample  Collection, Preservation, and Handling	7
8.0    Procedure	7
9.0    Quality  Control	11
10.0   Calculations / Results	12
11.0   Method Performance	13
12.0   References	14
13.0   Forms and Figures	16

Appendix A:  Example calculations for determining carbonate dissolution and pyrite oxidation rates ...A-1
Appendix B: Example calculations for estimating mineral solubility of calcite and gypsum	B-l
EPA Method 1627                                 ii                                   December 2011

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                                      Method 1627
   Kinetic Test Procedure for the Prediction of Mine Drainage Quality


1.0   Scope and Application

       Although acid-base accounting is widely used for coal mine drainage prediction, its applicability
       is limited to strata that have an appreciable net acid-base balance. Mines with near equal amounts
       of acid and alkaline production potential fall into a "gray" area that is difficult to predict. This
       gray area also includes some mines with low amounts of sulfur and carbonates, where it is
       difficult to predict whether water quality will be alkaline or acidic over time. Method 1627 is a
       standardized simulated weathering test that provides information that can be used to predict mine
       drainage quality that may occur from coal mining operations and weathering.  The method is
       intended for use in determining probable hydrologic consequences (PHC) and developing
       cumulative hydrologic impact assessment (CHIA) data to support Surface Mining Control and
       Reclamation Act (SMCRA) permit application requirements.  The method also can be a tool with
       which to generate data used to design and implement best management practices and treatment
       processes needed by mining operations to meet U.S. Environmental Protection Agency discharge
       compliance requirements at 40 CFR Part 434.

       The procedures in this method are directed toward the coal mining industry and regulatory
       agencies. The method also may be applicable to highway and other construction involving cut and
       fill of potentially acid-producing rock. This method originated under the auspices of the Acid
       Drainage Technology Initiative (ADTI) which is a consortium of scientists from federal research
       and regulatory agencies, state regulatory agencies, the mining industry and its consultants, and
       academia, who develop mine drainage technology through consensus building. The method has
       been referred to generically as the ADTI Weathering Procedure 2 (ADTI-WP2) in other
       publications. This method may be used in the laboratory to predict the water quality
       characteristics (e.g., pH, acidity, metals) of mine site discharges  using observations from sample
       behavior under simulated and controlled weathering conditions.  The method incorporates
       techniques similar to those already used into reproducible, documented, and validated procedures
       for widespread use. The method is based on procedures developed and evaluated in single,
       multiple and interlaboratory method validation studies using up to eight laboratories representing
       the mining industry, private sector, federal agencies, and academia.  Results of these studies are
       included in References 12.21 - 12.23.

       This method is performance-based which means that you may modify the procedures (with the
       exception of requirements indicated as "must") to improve performance (e.g., to overcome
       interferences or improve the accuracy or precision of the results) provided that you meet all
       performance requirements in this method. Requirements for establishing equivalency of a
       modification are in Section 11, Table 4, and are based on method performance in an
       interlaboratory method validation study, using datasets from seven laboratories, after outlier
       removal.  For Clean Water Act (CWA) uses, additional flexibility is described at 40 CFR 136.6.
       Modifications not in the  scope of Part 136.6 or in Section 11  of this method may require prior
       review and approval.

2.0   Method Summary

       The procedures described in this method include:  (a) the collection of representative samples, (b)
       preparation of samples, (c) controlled simulation of field weathering  conditions, and (d) leachate
       collection and analysis.
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       Samples are crushed to pass through a 3/8" wire mesh and characterized for neutralization
       potential,1 total (percent) sulfur, and particle size distribution.  Samples are reconstructed from
       particle size sieve separations to a specified particle size distribution (by percent weight), exposed
       to simulated weathering conditions, and periodically leached over time (at least 12 weeks) with
       CO2-saturated, deionized reagent water.  Throughout method implementation, a CO2-air mixture is
       added to the column and to the saturation water (leachate) to maintain a condition that is expected
       in the field.  The leachate is collected and tested for pH, conductivity, net acidity, alkalinity,
       sulfate, dissolved metals, and (depending on data needs) other analytes.

3.0    Limitations / Interferences

       The purpose of this method - to characterize the water quality of mine site drainage - is limited
       primarily by the extent to which the sample and simulated weathering conditions approximate
       actual site conditions.  The degree of representation is highly dependent on sample collection,
       storage, and preparation (crushing and particle size distribution) and on simulated weathering
       conditions (e.g., water handling, gas mixing, and saturation and drying cycles). This method,
       therefore, includes procedures needed to produce reliable prediction results under standardized
       conditions.

       When implementing this method and assessing method results, the user should consider sample
       collection and storage procedures, the changes made to the sample between collection and
       preparation (e.g., sample crushing and reconstruction), and the similarity of the simulated
       weathering to actual site conditions (e.g., percent humidity, partial pressures of gases, and
       saturation/drying cycles).  It is not possible to collect a sample from the field for evaluation in the
       laboratory without disrupting the in-situ particle size distribution through collection mechanisms
       and crushing. This method contains requirements to ensure that results represent standardized
       sample structure and weathering conditions.

        3.1     Surface Area to Volume Ratio- The ratio of the total surface area of the  sample to the
               volume of water that is added and collected during each saturation cycle can determine
               the extent to which water comes into contact with the  sample.

               3.1.1  In general, the column diameter should be a minimum of four times the diameter
                      of the largest particle (References 12.4 and 12.16).  This ratio is recommended
                      for samples with grain sizes exceeding 0.5 cm (0.2 inches). For smaller particles,
                      a factor greater than four should be used. Scaling factors that consider the ratio
                      of column dimensions and particle size are presented in Murr et al. 1911. This
                      method specifies a maximum sample particle  size of 3/8-inch (see Table 2 in
                      Section 8.1.3) and uses  2-inch diameter columns.

               3.1.2  This method contains a requirement and procedures for reconstructing samples
                      from sieved sample portions using a specific particle size distribution (by weight
                      percent) in the reconstructed samples. Reconstructed sample particle size
                      distribution is provided in Table 2.

        3.2     Surface Area - Although particle size distribution can be used to calculate surface area of
               a given sample, it often fails to indicate the total surface area that is, or can be, contacted
               by water in the column (i.e., soil particle surfaces can contain pores and other surface
               characteristics that are not recognized by sieve measurements).  If equipment is available,
1 Sobek, A.A.,W.A. Shuller, J.R. Freeman and R.M. Smith.  1978. "Field and Laboratory Methods Applicable to
Overburden and Minesoils."  U.S.EPA Report EPA-600/2-78-054 / Skousen, I, J. Renton, H. Brown, P. Evans, B.
Leavitt, K. Brady, L. Cohen and P. Ziemkiewicz. 1997.  "Neutralization potential of overburden samples containing
siderite." Journal of Environmental Quality. Vol. 26, pp. 673-681

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               the analyst may want to consider performing an assessment of particle surface area (e.g.,
               BET gas sorption analysis2).  This assessment provides information for determining rates
               in terms of mg/surface area/day (see Section 10.4.2).

       3.3     Sample Characterization and Leachate Analysis

               3.3.1  Given adequate carbonate minerals in the sample and sufficient contact time, the
                      water in the columns may reach saturation with respect to calcite at conditions
                      appropriate for 10% CO2. When the leachate is being drained, it will evolve
                      toward equilibrium with the air outside the column. This results in a degassing
                      of CO2 from the leachate and an increase in pH.  If the water was at or near
                      calcite saturation while in the  column, degassing of CO2 during collection of the
                      leachate may result in supersaturation of calcite in the leachate.  This process is
                      explained in Hornberger et al. (2003). This method describes procedures for
                      collection of leachate to minimize CO2 degassing (see Section 8.5.1).

               3.3.2  Additional potential interferences that may be encountered during leachate
                      analyses are specific to the analytical methods used to characterize the leachate.
                      These interferences and procedures for overcoming the interferences are
                      discussed in the individual analytical methods listed in Tables 1 and 3.

4.0   Safety

       4.1     This Method does not address all safety issues associated with its use. The laboratory is
               responsible for maintaining a current awareness file of OSHA regulations for the safe
               handling of the chemicals specified in this method or in the methods used to characterize
               samples (see Table  1) or analyze leachate (see Table 3).

       4.2     Each laboratory is responsible for maintaining a current awareness file of OSHA
               regulations regarding the safe handling of the chemicals specified in this method or in the
               methods that will be used to characterize samples (see Table 1) or to analyze leachate
               collected from the kinetic test columns (see Table 3). A reference file of Material Safety
               Data Sheets (MSDS) should be made available to all personnel involved in the chemical
               analysis.

       4.3     Extreme caution should be taken when handling pressurized gas cylinders  and the gas
               introduction procedures described in this method. Columns should be assembled and
               maintained in a hood, or otherwise well-vented area to control continuous venting of
               column off gases.

5.0   Apparatus and Materials

        Columns consist of vertical tubes or cylinders that are constructed to contain a sample of 3/8-inch
        maximum particle size and to allow for transport and/or holding of gases and water. An example
        column is presented in Figure  1. Water and/or gases are introduced into and drained from the
        bottom of the column to eliminate  air entrapment, simulate various groundwater conditions, and
        maximize contact with particle surface area.
 Brunauer, S., P.H. Emmett and E. Teller (1938). J. Amer. Chem. Soc. Vol. 60, p. 309 and (2) Yates, D.J.C. (1992)
"Physical and chemical adsorption-measurement of solid surface areas. In: Encyclopedia of Materials
Characterization: Surfaces, Interfaces, Thin Films." Edited by C.R. Brundle, C.A. Evans Jr. and S. Wilson, Boston,
MA: Butterworth- Heineman, pp. 736-744.


EPA Method 1627                                  3                                    December 2011

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       5.1     Column Apparatus - The column is constructed of a transparent polycarbonate or
               polystyrene cylinder with an inner diameter of 2 inches. Note: Use of polycarbonate,
               polystyrene or a similar transparent material is recommended so that sample conditions
               can be observed during addition of the sample to the column and throughout the
               weathering and leaching procedures.

               5.1.1   Column - 2-inch, clear, rigid, Schedule 40 PVC pipe, U.S. Plastic Part Number
                      34107, or equivalent.

               5.1.2   Column seals - Columns are sealed at the bottom, and include a removable cap
                      that contains a port for measuring and venting gases. 2-inch, clear, rigid,
                      Schedule 40 PVC fittings, Cap Slip, U.S.  Plastic Part Number 34296, or
                      equivalent. Used to seal the top and bottom of the column.

               5.1.3   Column Ports - Ports are inserted into the top and bottom of the column to allow
                      introduction of mixed gases and water, leachate collection, and gas venting.

                      5.1.3.1   Air/gas introduction and venting ports - Threaded / barbed elbows -
                               Nylon, thread %" NPT, Tube ID %" (U.S. Plastic Part Number 64301,
                               or equivalent) or polypropylene, thread %" NPT, Tube ID %" (U.S.
                               Plastic Part Number 64482, or equivalent)

                      5.1.3.2  Leachate drainage port - Nylon, threaded %" NPT, Tube ID 3/8" (U.S.
                               Plastic Part Number 64794, or equivalent)

               5.1.4   Column Tubing and Clamps - Column ports are connected to tubing that is
                      oriented to allow gravity flow of water into the column, drainage of water from
                      the column, and introduction and venting of gases (see Figure 1).  Clean flexible
                      tubing should be used to provide greater control of water and gas flow.
                      Recommended tubing sizes are 0.25" (gas mixture) and 0.5" (reagent water).
                      Tubing should be tied to the column port using a hose clamp or equivalent.

                      5.1.4.1   Vinyl tubing - Used for tubing that will not require clamping (e.g.,
                               manifold, gas lines, tubing from gas source to humidified gas
                               reservoir), %-inch ID and 3/8-inch OD, 1/16-inch wall thickness
                               (Fisher Scientific Part Number 141697C, or equivalent)

                      5.1.4.2  Rubber tubing - Used for tubing that will require clamping (e.g., water
                               introduction and drainage tubing, tubing from humidified gas reservoir
                               to column). Thick wall, rubber latex tubing, %-inch ID, 7/16-inch
                               OD,  3/32-inch wall thickness (Fisher Scientific Part Number 14-178-
                               5D, or equivalent)

                      5.1.4.3  Plastic tubing clamps - Used on latex tubing for quick, total shut off of
                               gases or fluids.  Fits 1/8-to !/2-inch tubing. (Fisher Scientific Part
                               Number 5869, or equivalent) OR Thermo pinch tight tube clamps
                               (McMaster-Carr Part Number 503 IK 13, or equivalent)

                      5.1.4.4  Fixed jaw clamps - Used on latex tubing to adjust gas flow (Fisher
                               Scientific Part Number 05870A, or equivalent)

                      5.1.4.5  Nylon Tees - Used to connect tubing. Tube ID  !/2-inch and %-inch
                               (U.S. Plastic Part Numbers 64349 and 64346, or equivalent)
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                      5.1.4.6  Couplers - Used to connect tubing. Tube ID %-inch, nylon or PVDF
                               (U.S. Plastic Part Numbers 64322 and 64437, or equivalent). Tube ID
                               !/2-inch, nylon (U.S. Plastic Part Number 64325, or equivalent)

               5.1.5   Column Lining - To allow uniform introduction of water and gases into the
                      column, the bottom (up to approximately 5% of the total  column height) contains
                      several layers of filter and support materials (refer to Figure 1). Reagent water
                      and gas mixtures are introduced through the plates, beads, and filter material and
                      into the sample via ports in the bottom of the column. These layers consist of 2
                      PVC/ polypropylene perforated plates, three layers of filter material (aquarium
                      filter media, and a 1.5-inch layer of 5/16-inch diameter acrylic or glass beads.
                      The layers should be added as presented in Figure 1 and are intended to trap the
                      smallest sample particle size, but not result in clogging.

                      Note:  Glass wool has been shown to neutralize acid and elevate pH in
                             experimental work at both the Minnesota Department of Natural
                             Resources and the US Bureau of Mines.  It should not be used in this
                             type of testing unless it is tested and shown to be unreactive.

                      5.1.5.1  Perforated Sheets - Polypropylene, Natural, 3/16-inch thickness, 3/16-
                               inch hole diameter, staggered rows (U.S. Plastic Part Number 42562,
                               or equivalent) OR PVC Perforated Sheets same thickness, diameter,
                               staggered rows  (U.S. Plastic Part Number 42562, or equivalent)

                      5.1.5.2  Plastic Beads - Polypropylene, !/2-inch diameter (U.S. Plastic Part
                               Number 91539, or equivalent) or HOPE, 5/16-inch diameter (U.S.
                               Plastic Part Number 91547, or equivalent)

                      5.1.5.3  Filter Pads - Marineland Bonded Filter Pads, 312 square inches. Cut
                               into circles to provide three filter pads to line column (Petco, Part
                               Number SKU:237531, or equivalent)

       5.2     Gas Mixture - Gases are mixed to a ratio of 90% air to 10% CO2 using either a certified
               gas mixture, two-stage gas cylinder regulators, flow meters, mixing valves (gas
               proportioners), or flow valves.  (Also see Section 6.1.)

               5.2.1   Gas introduction - Once mixed, gases are introduced into the reagent water in
                      the reagent water reservoir (Section 5.2.2) through a bubbler or porous stone
                      below the water surface.  The humidified gas mixture is maintained at the same
                      temperature as the column (i.e., 20 - 25°C +3°C, see Section 8.2.3) and is
                      introduced continuously through the column at a ratio of 9:1 (Air:CO2). See
                      Figure 2.

                      5.2.1.1  Gas monitoring - Gas flow must be introduced continuously to
                               maintain constant positive pressure, and must be monitored daily using
                               flow meters, gas meters, or tube indicators (e.g., Draeger tubes) to
                               ensure positive  flow and to ensure that the concentration of CO2 in the
                               outflow gas is at least 10%. (Bacharach Model No. 10-5000, with a
                               tolerance of ±0.5% or equivalent.)

                      5.2.1.2  Tubing clamps  - Fisher #05-871A (swivel jaw) or #05-870A (fixed
                               jaw), or equivalent, are used to control gas flow through the tubing
                               into the columns.  Use of a flow regulator and meter is recommended
                               to maintain a flow rate of approximately 1 L/minute of the mixed

EPA Method 1627                                 5                                   December 2011

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                               humidified gas into the column (e.g., Omega Model #FL3817-V
                               Rotameter or equivalent).

                      5.2.1.3  Rotameters - Capable of controlling the flow at approximately 1
                               liter/minute.  Rotameters should be used between the gas source and
                               the reagent water reservoir, and between the reagent water reservoir
                               and each column.  (TC-OMEGA Part Numbers FL-817-V or FL-815-
                               V, or equivalent.)

                      5.2.1.4  Tubing connectors - Threaded, barbed elbows, 0.12 x 0.25-inch, used
                               to connect rotameters to inlet and outlet tubing. (U.S. Plastic Part
                               Number 64758, or equivalent.)

               5.2.2  Reagent Water Reservoir - A water bottle or carboy is half filled with reagent
                      water (Section 6.2). The bottle is sealed with a rubber stopper containing inlet
                      and outlet ports for the introduction and release of the mixed gases (see
                      Figure 2).

                      5.2.2.1  Carboy - 2.5-Gallon  carboy. Carboys with handles provide support for
                               bungee cords needed to hold the stopper in place. (U.S.  Plastic Part
                               Number 75029, or equivalent.)

                      5.2.2.2  Rubber stopper - 2-hole, with third hole drilled into stopper at a
                               distance sufficient to allow bungee cord to  secure stopper in place once
                               tubing is inserted. (Thomas Scientific Part Number 8742S20, or
                               equivalent.)

                      5.2.2.3  Ridged tubing - 5/16-inch ID extruded ridged tubing, inserted into
                               holes in stopper to provide support for flexible tubing. Inlet and outlet
                               tubing is attached to  ridged tubing. (U.S. Plastic Part Number 44018,
                               or equivalent.)

                      5.2.2.4  Gas outlet port - Tubing is fitted through and just below the rubber
                               stopper into the headspace remaining in the reservoir.

6.0    Reagents

        6.1     Gas Mixture - A mixture of humidified air and CO2 at a ratio of 9:1.  This mixture is
               introduced continuously into the column (also see Section  5.2).

               6.1.1   Carbon dioxide (CO2) - Industrial grade. Gas cylinders or liquid CO2(i.e.,
                      Dewars) may be used.

               6.1.2  Air - Industrial grade compressed air at approximately 21% O2, 78 % N2.
                      Alternatively, house air may be used. Caution: The introduction of oil
                      contaminants into weathering columns can significantly affect the  results of this
                      method. If house air is used, it must be run through an in-line filter to ensure
                      that all oil is removed.

               6.1.3  An industrial grade  premixed compressed gas cylinder containing  O2:CO2:N2 at
                      a ratio of 1:1:8 may be used as an alternative to combining the gases in Sections
                      6.1.land 6.1.2.

        6.2     Reagent Water - Reagent water is prepared by distillation,  deionization, reverse osmosis,
               or other technique that removes potential interferences (e.g., metals and organics).

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       6.3     Reagents for Sample Characterization and Leachate Analysis - Reagents required for
               sample characterization and leachate analyses are specific to the analytical methods used,
               and are provided in the individual analytical methods listed in Tables 1 and 3.

7.0   Sample Collection,  Preservation, and  Handling

       7.1     Sample Collection - Collect representative bulk samples using air-rotary drilling, core
               drilling, or extraction from highwall, roadcut, or outcrop exposures. Collect samples
               using standard procedures described in Sobek etal., 1978;  Block etal, 2000; Griffiths,
               1967; and Tarantino and Shaffer, 1998. Approximately 2000 g of sample is needed to  fill
               a single column as described in this method.

       7.2     Documentation - Record the location, date, time, and amount of sample collected.

       7.3     Sample Crushing and Splitting - Prior to method implementation, bulk samples must be
               crushed to a maximum particle size of 3/8 inch.  To demonstrate the accuracy of results,
               it is recommended that at least two identical homogeneous sample aliquots  are prepared
               from each bulk sample (see Section 8.1.3).  Crush bulk samples into 3/8-inch size
               fractions using a jaw crusher. (The first portion of sample  that is crushed should be run
               through a screen or sieve to ensure the crusher is set to the  appropriate size.) After the
               entire sample is  crushed, it is riffled through a bulk splitter with openings set to
               approximately 1.5 inches, and split using a riffle splitter or other similar piece of
               equipment to get identical representative splits of the total  sample volume.  These
               procedures are described in ASTM C-702-98 and Noll et al, 1988.

       7.4     Sample Shipment. Storage, and Preservation - From the time of sample collection until
               method implementation, some oxidation of pyrite can occur, resulting in  soluble acid-
               sulfate salts.  Prior to method implementation, samples should be stored in sealed, HDPE
               containers, or some other airtight container, under dark, dry, and cool conditions.  For
               small sample sizes, opaque Nalgene bottles may be used. Crushed samples should not be
               stored for longer than six weeks. Sample shipment, storage, and preservation procedures
               are described in ASTM D5079.

8.0   Procedure

       8.1     Sample Preparation

               8.1.1   Sample Sizing - Pass the sample through a 3/8-inch mesh to ensure that no
                      particle sizes greater than 3/8 inch are added to the column (see Section 7.3).
                      Following this sizing, determine the particle size distribution of the sample using
                      at least five dry sieves (i.e., sieves No. 4, 10, 16, 35, 60).3  For analysis of
                      particle size distribution, use U.S. sieves or sieves of equivalent mesh size (e.g.,
                      U.S. #16 = Tyler #14).  Approximately 2 kg is needed for each column.

               8.1.2   Sample Characterization - Prior to method implementation, samples should be
                      analyzed for neutralization potential (NP) and percent total sulfur.  Methods for
                      analysis of these parameters are included in Table 1. If the overall change in
                      particle size, NP, percent sulfur, or other parameters will be determined, these
                      analyses also may be performed on the sample after the last leachate sample has
3 If additional information is needed to determine surface area or if method results will be used to determine reaction
rates in mg/surface area/day, the analyst may want to consider using additional sieves, Malvern system of laser
diffraction, or assessment of particle surface area (e.g., BET gas sorption analysis).

EPA Method 1627                                 7                                    December 2011

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                      been collected and the sample is removed from the column. [Note:  Additional
                      parameters may be measured if required or requested by the data user.]

                      Table 1:   Sample Characterization and Appropriate Methods

                      (Note:    Any approved ASTM, USGS, EPA, Association of Official Analytical
                               Chemists (AOAC), or Standard Methods analytical method may be
                               used for sample characterization)
Characteristic
Neutralization Potential
Total Sulfur
Method
Sobek, 1978 (EPA-600/2-78-054); Skousen et al. 1997
ASTM D3177, ASTM D4239, ASTM D2492
              8.1.3   Sample reconstruction - Once samples have been collected and crushed, sample
                      particle size distribution that occurred in the field is lost. The distribution
                      provided in Table 2 is intended to provide standardized conditions and to
                      facilitate uniform exposure of samples to weathering conditions and collection of
                      leachate. Using the sieved sample portions (see Section 8.1.1), reconstruct
                      samples into particle size distribution portions according to the weight
                      percentages specified in Table 2.

                      Table 2:   Particle size distribution of reconstructed samples
U.S.
Sieve # (or equivalent mesh size)
3/8" to 4
4-10
10-16
16-35
35-60
Less than 60
Total
Percent of Sample (by weight)
40
25
15
10
5
5
100
       8.2     Column Preparation

               8.2.1   Filling the Column - Uniform exposure of the sample to weathering conditions
                      is critical to method performance. Using a standardized rock density table (e.g.,
                      Blaster's Guide), determine the approximate total weight of sample needed to fill
                      the column to 4 inches below the top. Approximately 1800-2000 grams should
                      be sufficient to fill a column that is 2.5-feet in height and 2-inches in diameter.

               8.2.2   Using a wide-bore or powder funnel, add approximately 2,000 grams of the
                      reconstructed sample to the column, being careful to ensure uniform distribution
                      with little to no packing. (Note: The top of the sample should be at least
                      4 inches below the top of the column to prevent loss of sample or leachate water
                      during test implementation.) Weigh the sample before adding it to the column.

               Note:   The total weight of the sample added to the column must be recorded to the
                      nearest 1.0 gram, for use in results calculations.

       8.3     Column Maintenance

               8.3.1   Maintain the column at a temperature between 20 - 25°C + 3°C
                      (e.g., 22°C + 3°C).
EPA Method 1627
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               8.3.2   Check the column daily to ensure temperature and gas flow are maintained. An
                       example daily reporting sheet is provided in Section 13, Form 1.

                     8.3.2.1 The temperature must be recorded at least daily and remain constant. If
                             data will be used for assessment of reaction kinetics or gas mixture
                             partial pressure assessments, the data should be adjusted for temperatures
                             outside the range of 20 - 25 °C.

                     8.3.2.2 Using a portable CO2 meter (Section 5.2.1.1) capable of measuring CO2
                             to 10% (within + 0.5%), take daily readings of the CO2 released from the
                             column exhaust.

       8.4     Simulated Weathering Procedure - The simulated weathering procedures described in
               this section consist of alternating cycles of saturation and humidified gas mixture. These
               procedures are recommended for evaluation of overburden in non-arid regions or areas
               where there may be variably saturated conditions.  Alternative procedures may be used,
               provided they are designed to assess site conditions and meet the reproducibility
               performance standards included in Section 11.

               8.4.1    Initial Column Flush - Once the column has been filled with sample, reagent
                       water is introduced through the water inlet port (refer to Figure 1) until the
                       column is full and all visible pore  spaces are saturated. Gently tap the column to
                       fill any visible air pockets with water. Alternatively, a thin wire may be inserted
                       into the column to adjust the sample and ensure saturation. Allow the reagent
                       water to sit in the column for approximately 1 hour prior to collecting and
                       analyzing the initial flush water for conductivity.  Continue to add, drain, and
                       analyze reagent water in this manner until the conductivity of the water stabilizes
                       (relative standard deviation between conductivity measurements <20%).
                       Composite the collected flush water into a single composite water sample, and
                       analyze using the same procedures used to analyze the water samples collected
                       following each 24-hour saturation period (see Section  8.5).

               Note:    The volume of water added to and collected from the column should be recorded
                       with each flush.  These volumes also should be recorded during each weekly
                       saturation period.

               8.4.2   Humidified Air Cycles - Once the column has been drained of the final initial
                       flush sample, the humidified gas mixture (see Section  5.2)  is  introduced
                       continuously through the gas inlet port at the bottom of the column (see Figures
                       1 and 2). The column is allowed to sit for a period of 6 days during the
                       humidified air cycle. This cycle is repeated after each saturation cycle (Section
                       8.4.3).

               8.4.3   Saturation Cycles - Following each humidified air cycle, reagent water is
                       introduced through the water inlet port to just above the sample surface. If
                       necessary, gently tap the column to fill any visible air pockets with water. The
                       volume of water added must be recorded. If the introduction of water into the
                       column through the bottom port is difficult or slow, a pipette bulb can be used to
                       create a vacuum to pull water up and into the column.  Once water has been
                       added, clamp the water inlet tube shut, as close as possible to the column, to
                       ensure that the water collected at the end of the saturation period has been in
                       sufficient contact with the sample. Record the volume of water added to the
                       column.
EPA Method 1627                                 9                                    December 2011

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                      8.4.3.1   Gas Introduction - Once the column has been saturated according to
                                procedures in Section 8.4.3, introduce the gas mixture into the sample
                                through the gas inlet port at the bottom of the column until a slight
                                positive pressure is reached (i.e., a small outflow is produced through
                                the air vent in the top of the column).  Gas flow can be controlled and
                                maintained at approximately 1.0 L/minute using a combined flow
                                regulator and meter (e.g., Omega FL-3817-V Series Rotameter or
                                equivalent).

                      Note:   Care should be taken to avoid displacing the water during gas
                              introduction. Gas should be introduced slowly until slight positive
                              pressure is reached.

                      8.4.3.2 Leaching - Allow the column to sit for a period of 24 hours in  this
                              saturated condition. Following this 24-hour period, drain the column and
                              collect the leachate (see Section 8.5.1), then repeat the humidified air
                              cycle in Section 8.4.2).  The saturation cycle is repeated every week until
                              method implementation is complete (for up to a minimum of 12 weeks).

       8.5     Leachate Collection and Analysis

               8.5.1   Leachate Collection - Following each 24-hour saturation cycle, the
                      water/leachate is drained from the column and collected for analysis (Section
                      8.4.3.2).  Leachate  is drained from the column through the water inlet  tubing by
                      disconnecting the tubing from the water source.

               Note:   The procedure used to collect leachate must minimize carbon dioxide degassing
                      (e.g., insert the drainage tube into the bottom of the sample collection container
                      throughout collection; seal the container immediately following sample
                      collection; refrigerate the sample if analysis is not performed immediately; keep
                      sample container submerged in ice if collection drainage is slow).

                      8.5.1.1  The total volume added to and collected from each column must be
                              measured and recorded prior to water analysis. An example weekly
                              reporting sheet is provided in Section 13, Form 2.

                      8.5.1.2 Analyze the leachate immediately for determination of pH and
                              conductivity, and prepare additional aliquots for further analysis.  If the
                              leachate will be analyzed for dissolved parameters (SO4~2, metals), the
                              leachate must be filtered through a 0.45 (im filter prior to  analysis.

               8.5.2   Leachate Analysis - The leachate is analyzed for target parameters using
                      approved methods.  Recommended analytical methods are listed in Table 3.
                      Specific conductance (conductivity), alkalinity, and pH are analyzed as soon as
                      possible after collection. Leachate that will not be analyzed immediately for
                      measurement of other parameters  (e.g., metals, sulfate) must be preserved and
                      stored according to the requirements specified in the analytical method(s) to be
                      used.
EPA Method 1627                                 10                                    December 2011

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              Table 3:   Analytes and Appropriate Methods
              Note:   Any approved ASTM, USGS, EPA, AOAC, or Standard Methods analytical
                      method may be used for leachate analysis
Analyte
PH
Dissolved Metals **
(e.g., Fe, Mn, Al, Mg, Ca, Se)
Sulfate
Alkalinity (to pH 4.5)
Acidity / Net Acidity (to pH 8.2)
Specific Conductance
Method
EPA 150.1; Std. Methods 4500-H; ASTM D1293;
USGS 1-1 586
EPA200.7, 236.1, 236.2; Std. Method 3111, 3113,
ASTM D1 068; USGS 1-3381
3120;
EPA 375.1, 375.2, 375.4; Std. Methods 4500
EPA 31 0.1, 310.2; Std. Methods 2320B;
ASTM D1067; USGS 1-1030, I-2030
EPA 305. 1 ; Std. Methods 231 0; ASTM D1 067
EPA 120.1; Std. Methods 2510B; ASTM D1 125; USGS
1-1780
              ** The analytes measured will depend on specific permit needs or other intended uses of the data

9.0   Quality Control

        9.1    All quality control measures described in the referenced analytical methods for leachate
              analysis (Table 3) and sample characterization (Table 1) should be used.

        9.2    Blanks - Inert material (e.g., clean, well characterized quartz chips or sand of requisite
              particle size) is run along with samples to check for unexpected contributions from the
              test apparatus and reagents.

        9.3    Duplicate Samples - Duplicate samples are prepared according to procedures in Section
              8. Identical  sample masses and leaching volumes are used, and samples are exposed to
              identical simulated weathering conditions.

              9.3.1   At a minimum, at least one sample from each mine site must be run in duplicate.
                      If there are more than ten samples per site, then 10 percent of the total number of
                      samples must be run in duplicate.

              9.3.2   If necessary, the leachate from duplicate samples can be analyzed using a
                      staggered approach.  In this case, pH and conductivity are measured weekly from
                      both the primary and duplicate column. Analytes not requiring immediate
                      measurement (e.g., metals), are measured weekly in leachate from the  primary
                      column, but every other week in leachate from the duplicate column.

              9.3.3   Analysis of these samples gives a measure of the precision (relative percent
                      difference, RPD) associated with sample preparation and with laboratory
                      procedures. RPDs between results of duplicate samples are calculated for each
                      analyte (using Equation 1) and should not exceed the RPDs listed in Table 4.

                      Equation 1:   Relative Percent Difference between Duplicate Samples

                                           C1-C2
                                 RPD =
                                               C2)/2
       -*100%
                                 Where:
                                 Cl = concentration in primary sample
                                 C2 = concentration in duplicate sample
EPA Method 1627
11
December 2011

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10.0  Calculations / Results

        10.1  Analytical data should be reported initially in units of mg/L for aqueous (leachate)
              samples and mg/kg or percent for solid (overburden characterization) samples.  Results
              also may be reported in parts per thousand (ppt).

        10.2  Report total sample weight (Section 8.2.1) and leachate volume (Section 8.4.1).

        10.3  The mass of each analyte weathered from the sample each week can be calculated using
              Equation 2.

                             Equation 2:  Analyte Concentration in Samples


                      Analyte, mg =  ——  x (Leachate Volume Out, L)
                                     \ L )

        10.4  Acid production or metals release per weight of sample also can be determined by
              dividing the result in Section 10.3 by the weight of the sample exposed to weathering
              conditions.

       10.5  Evaluation of the weathering data can be performed to support permitting decisions and
              developing special handling plans for selected overburden strata. These data can be used
              alone or in combination  with data resulting from other mine drainage prediction tools
              (e.g. Acid/Base Accounting, X-Ray diffraction).  Typically, Acid/Base Accounting
              (ABA) (i.e., total sulfur  and neutralization potential) would be performed on all
              overburden  samples, and the weathering test described in this method would be
              performed on selected samples where the ABA was inconclusive.

              10.5.1  For permitting decisions the method can be used to determine whether
                      inconclusive samples have alkalinity exceeding acidity.  This is the most
                      fundamental question in evaluating overburden analysis  data. Using ABA, a
                      rock sample with a total sulfur content of 1% would have a Maximum Potential
                      Acidity (MPA)  of 31.25; if the rock sample had a NP of 31.25, it would be
                      interpreted that  the acidity and alkalinity would be equal or 0. The total sulfur
                      content is a surrogate measurement of the potential acidity and the NP is a
                      surrogate of actual alkalinity. The kinetic test method produces a leachate that
                      can be analyzed for the  actual acidity and alkalinity produced by the sample.

              10.5.2 Using ABA, it is not possible to obtain any measurement or accurate estimate of
                      the potential for production of iron, manganese, aluminum or other metal of
                      concern. The kinetic test method produces a leachate that can be analyzed for
                      any metal concentration. However, the user of the method should consider the
                      iron concentration, for example, to be an accurate and precise measurement of
                      the iron in the leachate, and not necessarily an accurate measurement of the
                      effluent from a  mine site.  In this respect, the iron concentration can be used to
                      indicate which rock samples may cause an iron problem on the mine site, and not
                      a number that should be compared to the effluent limitations for compliance
                      purposes.

              10.5.3 Since the weathering test is conducted for at least 12 weeks (see Section 2.0) or
                      longer if appropriate, a simple time plot should be constructed to determine if
                      there are any trends in the data. For example, plots of acidity and sulfate should
                      be made to determine if there is an increase through time that would indicate that


EPA Method 1627                                12                                   December 2011

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                      acid mine drainage is likely to be produced from that lithologic unit.  In addition,
                      time plots of alkalinity and calcium should be constructed to determine if there
                      are trends in the alkalinity or calcium data that would indicate that alkalinity
                      production or calcite dissolution is occurring from selected rock samples.

               10.5.4 Understanding the reaction kinetics of the rock samples weathering within the
                      leaching columns (and in the mine environment) is the ultimate goal of this
                      method. For example, if the sample is a shale from a marine paleoenvironment
                      with a pyritic sulfur content of 0.8% and a NP  of 80 tons per thousand tons of
                      calcium carbonate equivalents, does the weathering pattern have the
                      characteristic shape of a diffusion-controlled process (i.e., plot is the square root
                      of time)? Can we predict that the rate of pyrite oxidation will be offset by the
                      rate of calcite dissolution, and will the pyrite be depleted before the calcite?
                      (See References 12.3, 12.11, 12.12 and 12.24 and Appendices A and B).

11.0   Method Performance

        RPD results listed in Table 4 reflect the pooled results of the interlaboratory study, using datasets
        from seven laboratories evaluating the effects of weathering on samples of Brush Creek shale,
        Kanawha Black Flint shale, Lower Kittanning shale, Houchin Creek shale, and Middle Kittanning
        sandstone.  Method precision was assessed using results of duplicate samples exposed to identical
        weathering procedures.  RPDs were pooled for leachate samples collected over a 14-week period.

        Table 4:  Expected method precision (as RPD) based on Interlaboratory Study results
Analyte
Fe
Mn
Al
Ca
Mg
Se
Zn
Na
K
SO4
Alkalinity
Acidity
Conductivity

PH
14-week
RPD
90.4
52.5
72.5
21.9
21.4
42.9
60.2
25.1
23.7
27.5
28.7
99.9
13.2
Initial Flush
RPD
50.9
44.1
38.6
38.8
16.4
26.2
52.0
21.1
21.5
20.4
35.2
27.0
11.1
Weathering Test RPD
(Difference between 14-week and initial flush RPD)
39.5
8.4
33.9
(16.9)*
5.0
16.7
8.2
4.0
2.2
7.1
(6.5)*
72.0
2.1
Mean absolute difference
0.2
0.2
0
       * Relative percent difference between analyses were greater between samples collected during initial flush
       than between weekly samples.
EPA Method 1627
13
December 2011

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12.0  References

12.1   American Society for Testing and Materials (ASTM) D5744-96, Standard test method for
       accelerated weathering of solid materials using a modified humidity cell. In Annual book of
       ASTM Standards, 11.04. American Society for Testing and Materials, West Conshohocken, PA,
       pp. 257-269. 2000.

12.2   Block, Fred, J. Tarantino, R. J. Hornberger, K.B.C. Brady, J. Donovan, G. Sames and W.
       Chisholm.  Acid Drainage Technology Initiative (ADTI). Prediction of Water Quality at Surface
       Coal Mines. Chapter 6: Overburden Sampling Considerations.  December 2000.

12.3   Brady, K.B.C., R.J. Hornberger, B.E. Scheetz, and C.M. Loop.  Refinement ofADTI-WP2
       Standard Weathering Procedures, and Evaluation of Particle Size and Surface Area Effects Upon
       Leaching Rates. Part 2: Practical  and Theoretical Aspects of Leaching Kinetics, In Proceedings of
       21st National Conference - ASMR and 25th West Virginia Surface Mine Drainage Task Force
       Symposium, pp. 174-200. Lexington, KY. American Society for Mining and Reclamation. 2004.

12.4   Cathles, L.M. and K.J. Breen.  Removal of Pyrite from Coal by Heap Leaching. University Park,
       Pennsylvania State University, 103 p. 1983.

12.5   Geidel, Gwendelyn, F.T. Carruccio,  R. Hornberger, and K. Brady. Acid Drainage Technology
       Initiative (ADTI), Prediction of Water Quality at Surface Coal Mines. Chapter 5: Guidelines and
       Recommendations for Use of Kinetic Tests for Coal Mining (AMD) Prediction in the Eastern
       United States.  December 2000.

12.6   Griffiths, J.C. Scientific Method in Analysis of Sediments. New York: McGraw Hill Book Co.
       1967.

12.7   Hornberger, R.J., K.B.C. Brady, B.E. Scheetz, W.B. White and  S.C. Parson. ADT"I-WP2
       Leaching Column Method for Overburden Analysis and Prediction of Weathering Rates.  In:
       Proceedings of 26th West Virginia Surface Mine Drainage Task  Force Symposium, Morgantown,
       West Virginia, pp. 93-110. 2005.

12.8   Hornberger, R.J., K.B.C. Brady, W.B. White, B.E. Scheetz, J.E. Cuddeback, W.A. Telliard, S.C.
       Parsons, C.M. Loop, T.W. Bergstresser, C.R.  McCracken, Jr., and D. Wood. Refinement of
       ADTI-WP2 Standard Weathering Procedures, and Evaluation of Particle Size and Surface Area
       Effects Upohn Leaching Rates, Part  1: Laboratory Evaluation of Method Performance. In:
       Proceedings of 21st National Conference - ASMR and 25th West Virginia Surface Mine Drainage
       Task Force Symposium, pp. 916-947.  Lexington, KY. American Society for Mining and
       Reclamation. 2004.

12.9   Hornberger, Roger J.,  K.B.C. Brady, J.E. Cuddeback, W.A. Telliard, S.C. Parsons,  B.E. Scheetz
       and T.W. Bergstresser. Development of the ADTI-WP1 (Humidity Cell) and ADTI-WP2
       (Leaching Column) Standard Weathering Procedures for Coal Mine  Drainage Prediction,
       Proceedings from 2003 SME Annual Conference, February 2003.

12.10  Hornberger, Roger J. and K.B.C. Brady. Pennsylvania Department of Environmental Protection,
       Coal Mine Drainage Prediction and Pollution Prevention in Pennsylvania. Chapter 7 - Kinetic
       (Leaching) Tests for the Prediction of Mine Drainage Quality, October 1998

12.11  Langmuir, D. Aqueous Environmental Geochemistry, Upper Saddle River, New Jersey. Prentice
       Hall, Inc. pp. 600. 1997

12.12  Lasaga, A.C.  Kinetic Theory in the Earth Sciences, Princeton, New Jersey. Princeton University
       Press, pp. 811. 1998

EPA Method 1627                                 14                                  December 2011

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12.13  Murr L.E., L.M. Cathles, D.H. Reese, J.B. Hiskey, C.J. Popp, J.A. Brierly, D. Boss, V.K. Berry,
       W.J. Schlitt, and P.C. Hsu, 1977. Chemical, biological and metallurgical aspects of large scale
       column leaching experiments for solution mining and in situ leaching. In Situ, v.l, no. 3, pp. 209-
       233.1977.

12.14  Murr, L.E., Theory and practice of copper sulfide leaching in dumps and in-situ. Minerals
       Science and Engineering, v.12, no.3, pp.121-189.  1980.

12.15  Noll, D.A., T.W. Bergstresser, and J. Woodcock, Overburden Sampling and Testing Manual,
       Contract No. ME 86120, Pennsylvania Department of Environmental Resources, Bureau of
       Mining and Reclamation, 78 p. 1988.

12.16  Potter, G.M. Design factors for heap leaching operations.  Mining Engineering, v.33, pp 277-281.
       1981.

12.17  Skousen, J., A. Rose, G. Geidel, J. Foreman, R. Evans, W. Hellier, and Members of the
       Avoidance and Remediation Working Group of the Acid Drainage Technology Initiative (ADTI).
       A Handbook of Technologies for Avoidance and Remediation of Acid Mine Drainage. June 1,
       1998.

12.18  Skousen, J., J. Renton, H. Brown, P. Evans, B. Leavitt, K. Brady, L. Cohen, and P. Ziemkiewicz.
       Neutralization potential of overburden samples containing siderite. Jour. Environmental Quality,
       v. 26, pp. 673-681, 1997.

12.19  Sobek, A. A., W.A. Schuller, J.R. Freeman and R.M. Field and Laboratory Methods Applicable
       to Overburdens and Minesoils. EPA-600/2-78-054, 1978, 203 p. 1978.

12.20  Tarantino, J.M. and D.J. Shaffer, Planning the Overburden Analysis.  Chapter 5 in Coal Mine
       Drainage Prediction and Pollution Prevention in Pennsylvania. Pennsylvania Department of
       Environmental Protection, 1998.

12.21  U.S. Environmental Protection Agency, Development of Test Methods for Prediction of Coal
       Mine Drainage Water Quality, August 2002. Available from Joan Cuddeback, Computer
       Sciences Corporation, (703) 461-2025.

12.22  U.S. Environmental Protection Agency, Development of Test Methods for Prediction of Coal
       Mine Drainage Water Quality, September 2003. Available from Joan Cuddeback, Computer
       Sciences Corporation, (703) 461-2025.

12.23  U.S. Environmental Protection Agency, Results oflnterlaboratory Study for Evaluation of Draft
       ADTI- Weathering Procedure 2 (WP2): Column Test Method for Prediction of Coal Mine
       Drainage Water Quality, January 2003. Available from Joan Cuddeback, Computer Sciences
       Corporation, (703) 4611-2025.

12.24  White, W.B., Dissolution mechanisms of nuclear waste glasses.  In: A critical review, Nuclear
       Waste Management II, D.E. Clark, W.B. White and A.J. Machiels, Eds., American Ceramic
       Society, Advances in Ceramics, Vol, 20, pp 431-442. 1986.

12.25  Ziemkiewicz, P.P., Simmons, J.S. and Knox, A.S. The Mine Water Leaching Procedure:
       Evaluating the Environmental Risk of Backfilling  Mines with Coal Ash. In.  Sajwan, K. (ed.)
       Trace Elements in Coal Ash.  CRC Press. 2003.
EPA Method 1627                                 15                                   December 2011

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13.0  Forms and Figures
                                   Form 1:
                    Example Daily Monitoring Reporting Form
Sample ID:

Date/
Time








Temp.
°C








Column 1
Flow
(Lpm)








% C02
(in exhaust)








Column 2
Flow
(Lpm)








% C02
(in exhaust)









Notes








                                   Form 2:
                   Example Weekly Monitoring Reporting Form
Sample ID:
Date/
Time





















Week*
Initial
Flush
Week-1
Week-1
Week-2
Week-2
Week-3
Week-3
Week-4
Week-4
Week-5
Week-5
Week-6
Week-6
Week-7
Week-7
Week-8
Week-8
Week-9
Week-9
Week-1 0
Week-1 0
Water In
(mLs)





















Water Out
(mLs)





















PH





















Conductivity
(umhos/cm)





















Alkalinity
(to pH 4.5)
mg/L as CaCO3





















Acidity
(to pH 8.2)
mg/L as CaCO3





















EPA Method 1627
16
December 2011

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Figure 1:  Leaching Column
                                                               Air da\ \ cut
                2.5'
               21 total
             hcighl of
              packing
              nuicrul

«o 0^00*0 » o o o
O**o°*°oO O  *
       O  O   O   O O
                                                            Optional \\:nl to htHxl

                                                             Minimum vent diameter
                                                               air inlet diameter
                                                           Add .sample to approximately
                                                           4" below top of column
Filter Pad (aquarium filter media)
Perforated Plate(PVC' polypropylene)
» 1 (>" hole vli.iiiK.-k-r
Filter Pad
1.5" Layer of 5 1 ft" diameter acrylic beads
Filter Pad
Perforated Plate
                                                      	Flow Meter
EPA Method 1627
                    17
                          December 2011

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Figure 2:  Humidified Air/Gas
                                                                                              Two-stage
                                                                                              regulators
                                 Q
                     To column air/gas
                     inlet port
                      D.I. Water
EPA Method 1627
18
December 2011

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Appendix A: Example calculations for determining carbonate
                 dissolution and pyrite oxidation rates

Determining Carbonate Dissolution Rate

There are two ways to calculate carbonate dissolution.  Ultimately the rate of reaction is determined from
the amount of material that is weathered each week as a portion (or percentage) of the total of that
material that is in the rock. The examples below used acid-base accounting analyses of the Brush Creek
Shale (Table A-l). Material was obtained from four 5-gallon buckets of crushed, but not yet pulverized
rock.  Neutralization potential (NP) was determined two ways, the traditional Sobek et al. (1978) method
and the modified Skousen et al. (1997) method that takes steps to reduce the effects of siderite
interference. Siderite, a non-alkalinity generating carbonate can give falsely high NP readings if the
sample is not oxidized (Skousen et al., 1997; Cravotta and Rose, 1998). The Skousen method NP results
are about half the Sobek method results.  Field observations and mineralogy work performed by
Hammarstrom et al. indicate that the Brush Creek shale contains appreciable siderite. The Skousen
method NP numbers were used to determine the average NP for the Brush Creek Shale.

               Table A-1.  Acid-Base Accounting data for the Brush Creek Shale
NP Sobek
96.97
96.96
96.98
96.97
Avg 96.97
NP Skousen
49.68
49.31
47.61
47.07
Avg 48.42
%S
0.59
0.59
0.56
0.59
Avg 0.58
Although NP does not in and of itself specify the forms of carbonate, with the improved NP method of
Skousen et al. it is reasonable to assume that most of the NP is from carbonates that contribute to
neutralization.  For simplicity and accuracy, results are expressed as calcium carbonate equivalent.

Step 1. Determine the amount of calcium carbonate (equivalent) in the column.

Using the Average NP number (Table A-l) and the known mass of sample in a column, the amount of
calcium carbonate equivalent can be computed for the material in that column.  For example, Lab 5's
Column 1 contained 1879.2 grams of material. The units for NP are tons/1000 tons CaCO3 equivalent.
The amount of calcium carbonate equivalent contained in the column can be computed as follows:

                   1879.2  grams X (48.42/1000) = 91.0 grams CaCO3 equivalents

This number will be used to determine weathering rate.

Step 2. Determine the amount of calcium carbonate weathered each week.  This is done by determining
the mass of the weathering products produced each week in the leachate.  There are two ways this can be
done, the "cation approach" and the "anion approach" discussed below.

       Step 2a. The "Cation" Approach

The Cation Approach involves computations using the two cations that are commonly associated with
acid-neutralizing carbonates,  namely calcium and magnesium. These are evaluated in terms of calcium
carbonate equivalent by summing Ca as CaCO3 and Mg as CaCO3. Three assumptions are made:

(1) all Ca and Mg in solution are derived from carbonate dissolution,

(2) that Ca and Mg have not been lost from the solution and retained in the column, and (3) gypsum is not
present in the material being leached.
EPA Method 16271
A-l
December 2011

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If gypsum is present, then there is sulfate from a source that is not directly related to pyrite oxidation.
Thus, pyrite oxidation rate can not be accurately determined, unless one determines the amount of
gypsum dissolution per week and subtracts this portion.

    •  Assumption  1 .  By far the most common and most soluble mineral containing calcium on mine
       sites is calcite.  Other common sources of calcium are other carbonate minerals such as dolomite
       and ankerite. Magnesium is another common carbonate ion. Although there are other sources of
       Mg, the carbonates are by far the most soluble sources of Mg found in overburden rocks.

    •  Assumption 2.  The most common calcium-bearing mineral that is likely to precipitate from
       solution is gypsum. Gypsum solubility can be determined as shown in Appendix B. If gypsum is
       precipitating then some of the calcium that has dissolved will not be measured in the leachate, but
       in fact is being retained in the column.

    •  Assumption 3.  The presence of gypsum can be determined through hand sample observation, X-
       ray diffraction or other mineral determining techniques.

The mass of Ca and Mg leached each week can be determined from the mg/L of Ca and Mg leach
multiplied by the volume of leachate.


                       Analyte, mg =  — —  x (Leachate Volume Out, L)
                                     \ L )

The examples used below are of actual leachate obtained from the same column during the same week.
That is, all data are all from the same sample event.

Calculating CaCO^from Ca  The mass of calcium carbonate (equivalent) can easily be determined from
the mass of calcium.  The atomic weight of Ca is 40, and the molecular weight of CaCO3 is 100. Thus,
CaCO3 is 2.5 times the weight of Ca alone, and 40 grams of Ca converted to calcium carbonate equivalent
is 100 grams of CaCO3.  For example, a sample leaches 168 mg/L Ca and the volume drained from the
column is 385 mL.
                             176.0-^  x (0.279 L) = 49. 1 mg Ca
                     and

                           49. 1 mg Ca x 2.5 = 122.8 mg as CaCO3

Therefore, during this sample event  122.8 mg of CaCO3 equivalent weathered from the rock.

Calculating CaCO^from Mg The conversion of Mg to CaCO3 is the same process as that for calcium.
The atomic weight of Mg is 24.3. Dividing the molecular weight of CaCO3 of 100 by 24.3 gives a
conversion factor of 4. 1 .
                            I 83.1     I x (0.279 L) = 23.2 mg Mg
                            \      L )

                     and

                           23.2 mg Mg x 4. 1 = 95.0 mg as CaCO
                                                                3
EPA Method 16272                              A-2                                  December 2011

-------
Calculating CaCO3 from Ca + Me The next step is to simply combine the calcium carbonate equivalents
calculated above:

                       122.8 mg Ca + 95.0 mg Mg = 217.8 mg as CaCO3

Therefore, during the course of the previous week, 217.8 mg of carbonates, measured as CaCO3
equivalent, were dissolved.

        Step 2b. The "Anion" Approach

The Anion Approach involves determining excess alkalinity and neutralized alkalinity produced by
evaluating two anions that are commonly associated with neutralized mine drainage, bicarbonate and
sulfate.  The sulfate part of the equation, is not necessarily intuitive and requires some explanation.  This
approach only works where a water is net alkaline. It will not work for acidic samples. Again,
assumptions are made: (1) sulfate has not been lost from the solution and retained in the column, and (2)
gypsum is not present in the rock.

    •   Assumption 1 .  The most common sulfate-bearing mineral that is likely to precipitate from
        solution is gypsum.  Gypsum solubility can be determined as shown in Appendix B.  If gypsum is
        precipitating then some of the sulfate that has dissolved will not be measured in the leachate, but
        in fact is being retained in the column.

    •   Assumption 2.  The presence of gypsum can be determined through hand sample observation or
        X-ray diffraction or other mineral determining techniques.

Bicarbonate alkalinity.  Bicarbonate alkalinity is generally reported as CaCO3 equivalent, so no
conversion is necessary. If it is not reported as CaCO3 equivalent, HCO3 can be converted to CaCO3
using the following equation:

                               mg/L HCO3 x 0.8202 = mg/L CaCO3

Determining milligrams of CaCO3 is performed using the same process as that for calcium and
magnesium discussed above, except no conversion is typically necessary to obtain calcium carbonate
equivalent. Using the same sample event as the examples above, the concentration of alkalinity as CaCO3
was 520 mg/L.
                           I 520 ^ I x (0.279 L)= 145.1 mg CaCO3
                           \     ^ J

Alkalinity Neutralized The alkalinity measured in a mine water is the "excess" alkalinity that has been
produced. In samples with pyrite oxidation occurring, some alkalinity has been neutralized by the acid.
The amount of acidity that has been produced can be calculated based on the following stoichiometry:

                       FeS2 + 3.25 O2 + 3.5 H2O = Fe(OH)3 + 2 SO42 + 4 H+

For every mole of pyrite oxidized there are 2 moles of sulfate produced and 4 moles of FT. It takes 2
moles of CaCO3 to neutralize 4 FT. This relationship can be written as:

                           4 mol FT   = 2 mol CaCO3 = 200 g CaCO3
                           2 mol SO42-    2 mol SO42 ~      192 g SO42


Therefore, for every 1 mg/L (or gram) of sulfate, 1.04 mg/L (or gram) of acidity, as CaCO3, are produced.
EPA Method 16273                                A-3                                   December 2011

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Therefore, if a sample is net alkaline, the neutralized alkalinity can be calculated from sulfate, by using
the following equation:

                                mg/L SO4 x 1.04 = mg/L CaCO3

       Using a sulfate value of 235 mg/L, we get:
             298 —2- x 1.04  x (0.279 Z,) = 86.5 mg neutralized alkalinity as CaCO3
            \     L       )
Calculating CaCO^from Alkalinity + Sulfate The next step is to simply combine the calcium carbonate
equivalents calculated above:

       141.1 mg Alkalinity CaCO3 + 86.5 mg neutralized alkalinity = 227.6 mg as CaCO3

Therefore, during the course of the previous week, 227.6 mg of carbonates (measured as CaCO3
equivalents), were dissolved. We had calculated earlier that there is a total of 91.0 grams of CaCO3
equivalent in the column. Thus, during this one week:


                         I °'2276 g I x 100 = 0.25% CaCO3 weathered
                         l91.0gj

Step 2 c.  Compare the two methods. Figure A-l compares the percentage CaCO3 equivalent leached at
the end of 14 weeks for data from four of the laboratories used in this study. The two methods compare
favorably in all cases except for the HCS-IN sample after it went acidic. When a sample goes acidic only
the "cation" approach is appropriate because the acidity (measured from sulfate) has not all been
neutralized.
EPA Method 16274                               A-4                                  December 2011

-------
                      'o
                      c
                          40-r
                          35	
30	
+
o
n
o
A
HCS-IN
LKFC-PA
KBF-VW
BCS-PA
MKSS-PA
                                           10     15     20
                                      % CaCOs from Ca + Mg

Figure A-l. Comparison of the "anion" and "cation" methods of determining carbonate dissolution. The
cumulative value at the end of 14 weeks leaching was used to construct this plot.  As can be seen, most
data fall on or near the diagonal line, which represents where data would fall if both methods produce the
same answer. The circled values indicate columns that became acidic.

Determining Pyrite Oxidation Rate

Pyrite oxidation rate is determined from the amount of sulfur weathered each week. This is then
compared to the mass of sulfur in the rock. The sulfur in the rock is determined during acid-base
accounting.  The examples below are analyses of the Brush Creek Shale and are for the same leaching
event used above. The average sulfur shown in Table A-l was used for calculations.

Step 1. Determine the amount of sulfur in the column from the average of the samples analyzed.

Using the average percent sulfur value (Table A-l) and the known mass of sample in a column, the
amount of calcium carbonate equivalent can be computed for the material in that column. For example,
Lab 5's Column 1 contained 1879.2 grams of material. The amount of sulfur contained in the column can
be computed as follows:

                            1879.2 grams X (.0058) = 10.9 grams sulfur

For the purposes of this study we used total sulfur values.  There are multiple known problems with using
forms of sulfur (Brady and Smith, 1990) for coal overburden samples. Pyrite is 53.45% sulfur, so to
determine the amount of pyrite in a rock the percent sulfur can be multiplied by 1.873:

                                0.58% S X 1.873 = 1.09% pyrite

Step 2. Determine the sulfur oxidation rate.
EPA Method 16275
                   A-5
December 2011

-------
Sulfur has an atomic weight of 32. Sulfate has an ionic weight of 96 (32 + (16 x 4) = 96).  Thus, sulfur
comprises one-third the weight of sulfate. To calculate the amount of sulfur leached each week use the
following equation:

                       29Smg/LS04                      ^ weathered
To determine the percentage of the available sulfur that was weathered during this time period use the
following equation:


                             °'°277 g I x 100 = 0.25% S weathered
                            (  10.9 g J

Thus the weathering rate of the pyrite is similar to that for the carbonates during this particular weathering
cycle.

Cumulative Weathering Rate

The above calculations are done for each week. The only reasonable way to do the multiple calculations
for each column and for each week is to us a spreadsheet. The types of calculations presented in
spreadsheet format are displayed in Table A-2. The percentage weathered each week can be added
cumulatively to determine the amount of carbonate or sulfur weathered through the duration of the test.
This also allows for the evaluation of whether or not the rate of weathering changes throughout the course
of the test.  If a rate is beginning to dramatically accelerate, the test should probably be extended in
duration. The graphs that follow are from Table A-2 data.

Comparisons of cumulative weathering rates can show which suite of minerals is weathering faster, the
carbonates or the sulfides.  Best-fit lines can be fitted to the data to predict weathering into the future. If
the sulfides are exhausted before the carbonates, the rock will likely produce excess alkalinity well into
the future.  If carbonate minerals are exhausted first, especially if this happens quickly, the rock  will
likely go acidic with time.
EPA Method 16276                               A-6                                   December 2011

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Table A-2. Example table of the computational steps to determine CaCO3 weathering rate. Column 1 identifies the week that was leached. Week "0"
           is the initial flush. Weeks 1 through 14 are the actual weeks that the sample is weathered. Column 2 is the leachate volume collected.
           Column 3 is mg/L calcium. Column 4 is the mg calcium computed from columns 2 and 3. Column 5 is the mg calcium displayed
           cumulatively.  Column 6 is calcium displayed as calcium carbonate. Columns 7 through 10 are the same as those described above, but for
           magnesium. Column 11 is the sum of columns 6 and 10.  Column 12 is column 11 divided by the total mass of calcium carbonate
           equivalent in the column, expressed in percent.
1
Week
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
2
Vol
Out
mL
1356
310
340
295
309
270
279
296
285
285
268
260
260
274
264
3
mg/L
Ca
99.8
270.0
240.0
186.0
175.0
170.0
176.0
147.0
153.0
163.0
156.0
142.0
148.0
162.0
151.0
4
mg Ca
135.33
83.70
81.60
54.87
54.08
45.90
49.10
43.51
43.61
46.46
41.81
36.92
38.48
44.39
39.86
5
Cumulative
mg Ca
135.33
219.03
300.63
355.50
409.57
455.47
504.58
548.09
591.69
638.15
679.96
716.88
755.36
799.75
839.61
6
Cumulative
mg Ca as
CaCOS
338.32
547.57
751.57
888.75
1023.93
1138.68
1261.44
1370.22
1479.24
1595.37
1699.89
1792.19
1888.39
1999.36
2099.02
7
mg/L
Mg
57.1
148.0
131.0
93.3
82.7
78.8
83.7
68.7
68.4
84.3
68.6
62.7
59.8
68.7
66.4
8
mg Mg
91.83
54.41
52.82
32.64
30.31
25.23
27.70
24.12
23.12
28.49
21.80
19.33
18.44
22.33
20.79
9
Cumulative
mg Mg
91.8
146.24
199.07
231.71
262.02
287.25
314.95
339.06
362.18
390.68
412.48
431.82
450.26
472.58
493.37
10
Cumulative
mg Mg as
CaCOS
377.90
601.82
819.20
953.53
1078.25
1182.09
1296.07
1395.32
1490.46
1607.72
1697.45
1777.01
1852.90
1944.77
2030.32
11
Cumulative
Ca + Mg as
CaCOS
716.22
1149.39
1570.77
1842.28
2102.19
2320.78
2557.51
2765.54
2969.70
3203.09
3397.34
3569.21
3741.29
3944.13
4129.35
12
% CaCOS
weathered
each week
from 91 .0 g
0.79
1.26
1.73
2.02
2.31
2.55
2.81
3.04
3.26
3.52
3.73
3.92
4.11
4.33
4.54
EPA Method 16277
A-7
December 2011

-------
                                      Graphing the Data

The first thing that one should do with the data is graph the concentrations. This will allow one to spot
obvious trends and errant values. Figures A-2 through A-6 shows actual data and calculated values from
one of the columns from one of the laboratories used in the interlaboratory method evaluation study
(Method 1627 Reference 12.23).

                        300-,
                        250-
                      O)
                     •§ 200-
                      o
                     '-4—'
                      CO
                      g 150'
                      o
                     O
                        100'
                         50'






                                \   \    \   \   \   \   \   \   \   \   \   \   \   \
                             0  1   2  3  4   5   6   7   8   9  10  11  12  13  14
                                                Week

Figure A-2. Concentration of calcium and magnesium through the "initial flush" (week 0) to week 14.

                         160-1
                         120-
                       CD
                       o
                       D)
                       E  80-
                       CD
                       O
                       X
                       il  40 H
                                                             Calcium
                                                             Magnesium
                                 \   \   \   \   \   \   \   \   \   \   \   \   \  \
                              0  1   2   3   4   5   6   7   8   9  10 11  12 13 14
                                                Week
Figure A-3. Flux (load) of analyte.
EPA Method 16278
A-8
December 2011

-------
                        1000-r
                     co   800--





*
                     o

                     O)
                     T3
                     CD
                     O
                         600--
                     =   400--
                     cu
                     ,>
                     '-4—'
                     _CO
                     3

                     E
                     ^
                     O
200 ---?*-
                                 \\   \   \   \   \   \   \   \   \   \   \   \   \

                              0   1   2   3   4   5   6   7   8   9  10 11 12 13 14

                                                Week
Figure A-4. Cumulative flux (load) of analyte over the 14 week period.


                        5000 —r
                     CO
                     o
                     O

                     CO
                     co

                     O)

                     E
                     T3
                     CO
                     _0
                        4000 - -
                        3000 - -
	 ^ 	 Calcium
— + 	 Manganese
— • 	 Ca + Mg

                     =  2000 - -
                     0)

                     "•p
                     _co
                     D

                     E
                     D
                     O
        \   \   \   \   \   \   \   \
     0  1   2   3   4   5   6   7   8
                       Week
                                                         \   \   \   \   \   \
                                                         9  10 11 12 13 14
Figure A-5. Cumulative flux of calcium and magnesium expressed as calcium carbonate. Also plotted is

the flux of total calcium carbonate equivalent (Ca + Mg).
EPA Method 16279
                    A-9
December 2011

-------
                                               1   I   I   I   I   I   I   I   I
                                               6   7   8   9  10 11 12 13 14
                                               Week

Figure A-6. Percentage of calcium carbonate equivalent weathered through the course of the leaching
test. In this instance, approximately 4.5% of the calcium carbonate (equivalent) was removed from the
column during the weathering test.
EPA Method 162710
A-10
December 2011

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Appendix A References

Brady, K.B.C. and M.W. Smith, 1990. Pyritic sulfur analyses for coal overburden: Differences between
laboratories. In: 1990 National Symposium on Mining, University of Kentucky, Lexington, KY, pp. 53-
58.

Hammarstrom, J.M., C.A. Cravotta III, D. Galeone, J.J. Jackson, K.B.C. Brady and F. Dulong, (in press).
Characterization of rock samples and mineralogical controls on leachates. USGS

Rose, A.W. and C.A. Cravotta III, 1998.  Geochemistry of coal mine drainage.  Chapter 1, In: Coal Mine
Drainage Prediction and Pollution Prevention in Pennsylvania; K.B.C. Brady, et al, eds. PA Dept.
Environmental Protection, p. 1.1-1.22.

Skousen, J., J. Renton, H. Brown, P. Evans, B. Leavitt, K.B.C. Brady, L. Cohen, and P. Ziemkiewicz,
1997. Neutralization potential of overburden samples containing siderite. Journal of Environmental
Quality, Vol. 26, pp. 673-681.

Sobek, A., W. Schuller, J. R. Freeman, and R. M. Smith, 1978. Field and Laboratory Methods Applicable
to Overburdens and Minesoils. Prepared for U.S. Environmental Protection Agency, Cincinnati, Ohio.
EPA-600/2-78-054, 203 p.
EPA Method 162711                              A-l 1                                 December 2011

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Appendix B: Example calculations for estimating mineral solubility of
                 calcite and gypsum

Mineral Solubility

Given sufficient time and stable conditions, a mineral will dissolve in water, up to the point where the
water cannot "hold" any more of that mineral's constituents. This characteristic solubility relation for a
mineral can be evaluated by an equilibrium equation and constant, assuming the system is at or near
chemical equilibrium. For many rock-water reactions, the equilibrium assumption is reasonable.  A
precipitation / dissolution reaction can be written into a chemical reaction expression as follows:

                                   wA + xB  ^ _ ^.yC + zD

        Where:  A, B, C and D are products and reactants, and w, x, y and z are stoichiometric
        coefficients. Gypsum and calcite dissolution/precipitation reactions are:

                    CaSO4 *2 H2O + — * Ca2+ +   SO42   +  2 H2O

                            CaCO3  ^ — >  Ca2+  + CO32

The chemical reaction can be formulated into a mathematical expression as follows:
        Where: the brackets represent chemical activity in moles/L, and K° is an equilibrium constant
        characteristic for the reaction. Values for equilibrium constants are experimentally determined at
        specific temperatures, usually 25°C. The van't Hoff equation is used to correct the value of K°
        at temperatures other than 25 °C.

At equilibrium, gypsum and calcite solubility are represented as:

                                                                 ^
                            a,2

                     and

                           [c
-------
     •   S.I. less than zero(O), indicates the water is under-saturated for the mineral, or is holding less
        than the maximum it can contain of that mineral's constituents. The mineral cannot precipitate
        from the water.  If the mineral is present in the rock, it could dissolve into the water.

     •   S.I equal zero(O), indicates the water is saturated for that mineral. The water has dissolved all of
        that mineral's constituents that it can hold, and is at equilibrium for that mineral.

     •   S.I. greater than zero(O) indicates the water is over-saturated for that mineral.  The water has
        more of the mineral's constituents  than it can hold, and the solid mineral should precipitate.
The equilibrium constant K° is usually determined on mineral phases that are pure, or of known
composition. Some minerals such as calcite may have other elements substituted in the crystal lattice.
Calcite can contain a few percent magnesium, iron, strontium or other elements in place  of calcium.
Solubility of these mixed phases can be different than the pure mineral. Even for pure mineral phases,
reported equilibrium constants often have a range of experimental uncertainty.

The products and reactants in solubility calculations are expressed as chemical activities or "effective
concentration." In very dilute waters, activity and total concentration are  nearly the same.  However, as
ionic strength of a water increases, charged ions interact and the effective and total concentrations
diverge.  The difference between chemical activity or "effective concentration," and total concentration
depends on ionic strength.  The chemical activity is calculated from estimates of ionic  strength, ion size
and charge and total concentration in several steps.

The first step is calculating ionic strength, which is a measure of the electrical charge present in solution.
It is calculated as:
        Where:  mi is molar concentration, and z. is charge on the ion. The charge is summed for each
        measured cation and anion.

It is possible to estimate ionic strength from specific conductance measurements; however, those
estimates can be less precise.

The second step is to calculate an activity coefficient using either the Debye-Huckel or Davies equations.

                                log 7. = -Az^-Jl  (Debye-Huckel)
                               log Yi = - l—f= -- 0.3x7  (Davies)
                                         1 + V/
        Where: A is a constant, I is ionic strength, and yjis the activity coefficient. The Davies equation
        is considered accurate up to ionic strengths of about 0.5 molar.

Chemical activity and total concentration are related to each other by the activity coefficient y; as follows:

                    Activity Coefficient (y; ) =  (Chemical Activity / Concentration)

Activity coefficients are usually less than one, and chemical activity and total concentration are expressed
in mol/L.  The coefficient permits conversion of the total concentration values into activity units needed
for solubility calculations.  The activity of a solid in the calcite and gypsum reactions is defined as 1, and
the amount of water involved in reaction is small relative to the bulk solution, that the activity of water is


EPA Method 1 6272                                 B-2                                    December 20 1 1

-------
also 1 or nearly so.  Mineral solubility concepts are described in more detail in the references listed at the
end of this appendix.

Software for Calculating Gypsum and Calcite Solubility

Saturation indices for calcite and gypsum can be calculated using the US EPA geochemical code,
MINTEQA2, or the US Geological Survey software, PHREEQCI.  These software are equilibrium
speciation models that calculate the composition of dilute aqueous  solutions in laboratory, surface or
ground water systems, including the distribution among dissolved,  adsorbed, and solid phases under
specified gas composition. This software includes a choice of several comprehensive data bases for
modeling,  and both models solve iteratively for equilibrium composition to a specified level of precision.
Commercial software, such as Geochemist Workbench, is also capable of performing these calculations.
The model computations follow the techniques for chemical activities and equilibrium constants
described in the first section of this appendix.

    •   MINTEQA2 and corresponding documentation can be obtained at EPA's Center for Exposure
       Assessment Modeling, Multimedia Models, at: http://www.epa.gov/ceampubl

    •   PHREEQCI and corresponding documentation can be obtained from the USGS Water Resources
       Division, Geochemical Software at: http://water.usgs.gov/software/lists/geochemical

The recommended parameters for calculating gypsum and calcite solubility are:  pH, alkalinity,
temperature, calcium, sulfate, magnesium, sodium, potassium, iron, aluminum, manganese.  Magnesium,
sodium, potassium, iron, aluminum or manganese can be omitted if these parameters are known to be
present only in small concentrations (< about 10 percent of the total cation charge).

Mineral solubility can also be computed in spreadsheets.

Example Calculation of Gypsum and Calcite Solubility

Gypsum and calcite solubility were calculated for the five standard rock samples using PHREEQC and
MINTEQA2. The two software produce near identical results with only very minor differences due to
rounding and significant figures. Table B-l shows the leachate composition data and computed saturation
indices for sample BCS3-PA from one lab. Gypsum and calcite saturation indices were calculated for
each weekly sample, and results are plotted in Figure B-l  for 12 weeks.
Calcite and Gypsum Saturation Indices, Sample BCS3-PA
Oc
.0
Oc
.0
•1
,5

j* '~^~' *x~ _ _^> — "^\^
*
^\
^^^^-t t ^ ^
I - |
II 1 1 1 1 1 1 1 1 1 1 1 II
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Week

—•—Calcite
— • — Gypsum

        Figure B-l. Calcite and Gypsum Saturation Indices, Sample BCS3-PA
EPA Method 16273
B-3
December 2011

-------
    This rock is approximately at equilibrium for calcite throughout the test period. Calcite is dissolving
    into the leach water up to the maximum amount of carbonate alkalinity and calcium that the water
    can" hold." The aqueous concentrations of these two parameters are constrained by the solubility of
    calcite.

    The leachate samples are under-saturated for gypsum throughout the entire test period.  The mineral
    gypsum cannot form a solid precipitate from these waters. The aqueous concentrations of calcium
    and sulfate are not constrained by gypsum solubility. Because the saturation index is in log base 10,
    the plot shows that after week two, the water is under-saturated for gypsum by a factor of greater than
    10. If gypsum is present in the rock, it could dissolve into solution.
    Table B-1:    Leachate Composition for Sample BCS3-PA for 12 weekly samples
                                                                                 d)
Week
1
2
3
4
5
6
7
8
9
10
11
12
PH
7.20
7.24
7.33
7.32
7.29
7.34
7.18
7.14
7.23
7.18
7.15
7.02
Alkalinity
198.5
222.7
239.2
229.1
249.3
220.5
221.9
252
230.9
264.9
220.3
259.3
Temperature
20.8
21.8
21.5
22.4
21.9
21.5
22
21.1
20.4
21.9
22
22.2
Ca
204
121.5
102.5
99.2
93.9
81.4
74.7
90.8
77.8
103.4
75.7
99.7
Mg
103.8
68.6
57.6
53.8
38.1
33.2
31.8
40.7
33.6
44.7
27
33.5
Sulfate
678
392
270
203
162
135
147
133
110
137
112
148
Na
11.3
6.9
5.0
2.8
2.4
1.4
2.3
2.4
1.7
1.7
1.5
1.5
K
6.1
6.5
5.7
4.4
4.3
4.3
3.2
3.9
3.9
3.5
3.4
2.2
Calcite
S.I.
0.13
0.09
0.17
0.16
0.16
0.11
-0.08
0.00
-0.01
0.12
-0.09
-0.06
Gypsum
S.I.
-0.65
-0.99
-1.17
-1.29
-1.37
-1.47
-1.47
-1.46
-1.57
-1.41
-1.56
-1.37
   (1) pH in S.U., alkalinity in mg/L CaCO3 ,temperature in C°; Ca, Mg, sulfate, Na and K in mg/L, calcite and
   gypsum indices are dimensionless.

   S.I. is saturation index
Appendix B References

Appelo C.A.J. and D. Postma, Geochemistry, Groundwater and Pollution, 2nd ed, Leiden, Netherlands,
Balkema, pp 649. 2005.

Langmuir, D. Aqueous Environmental Geochemistry, Upper Saddle River, New Jersey. Prentice Hall,
Inc. pp. 600. 1997.

Stumm, W. and J.J. Morgan, Aquatic Chemistry, Chemical Equilibria and Rates in Natural Waters, 3rd
ed., New York, New York, John Wiley and Sons Inc, pp 1022, 1996.
EPA Method 16274
B-4
December 2011

-------