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
-------
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
-------
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
-------
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
-------
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.
EPA Method 1627 1 December 2011
-------
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
EPA Method 1627 2 December 2011
-------
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
-------
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)
EPA Method 1627 4 December 2011
-------
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
-------
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).
EPA Method 1627 6 December 2011
-------
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
-------
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
December 2011
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
Figure 2: Humidified Air/Gas
Two-stage
regulators
Q
To column air/gas
inlet port
D.I. Water
EPA Method 1627
18
December 2011
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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 = - lf= -- 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
------- |