United States Office of Water

Environmental Protection Agency (4303) December 2011

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 
EPA Method 1627 i December 2011

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 ii December 2011

Table of Contents

1.0 Scope and Application ..................................................................................................................... 1

Page

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-1
EPA Method 1627 1 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 2 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

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. 1977. 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.

– 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. 

3.1.2 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

 

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, J., 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

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, 
EPA Method 1627 3 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

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).

Sample Characterization and Leachate Analysis

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.

 

2 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 4 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

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

34107, or equivalent. 

: 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.

5.1.2 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 1⁄4” NPT, Tube ID 1⁄4” (U.S. Plastic Part Number 64301, 

or equivalent) or polypropylene, thread 1⁄4” NPT, Tube ID 1⁄4” (U.S. 

Plastic Part Number 64482, or equivalent) 

5.1.3.2 Leachate drainage port - Nylon, threaded 1⁄4” 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). 1⁄4-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. 1⁄4-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 1⁄2-inch tubing. (Fisher Scientific Part 

Number 5869, or equivalent) OR Thermo pinch tight tube clamps 

(McMaster-Carr Part Number 5031K13, 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 1⁄2-inch and 1⁄4-inch 

(U.S. Plastic Part Numbers 64349 and 64346, or equivalent) 
EPA Method 1627 5 December 2011

5.1.4.6 Couplers - Used to connect tubing. Tube ID 1⁄4-inch, nylon or PVDF 

(U.S. Plastic Part Numbers 64322 and 64437, or equivalent). Tube ID 

1⁄2-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

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) 

: 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. 

5.1.5.2 Plastic Beads - Polypropylene, 1⁄2-inch diameter (U.S. Plastic Part 

Number 91539, or equivalent) or HDPE, 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 

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. 

– 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.) 

5.2.1.1 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 6 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

6.1.1 Carbon dioxide (CO2) – Industrial grade. Gas cylinders or liquid CO2 (i.e., 

Dewars) may be used.

 – 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). 

6.1.2 Air – Industrial grade compressed air at approximately 21% O2, 78 % N2. 

Alternatively, house air may be used. Caution

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 

6.1.1 and 6.1.2.

: 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.

6.2 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 7 December 2011

6.3 Reagents for Sample Characterization and Leachate Analysis

7.0 Sample Collection, Preservation, and Handling

 – 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. 

7.1 Sample Collection

7.2

- 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 et al., 1978; Block et al., 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. 

Documentation

7.3

 – Record the location, date, time, and amount of sample collected. 

Sample Crushing and Splitting

7.4

 – 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. 

Sample Shipment, Storage, and Preservation

8.0 Procedure

 – From the time of sample collection until 

method implementation, some oxidation of pyrite can occur, resulting in soluble acidsulfate 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.

8.1

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. 

Sample Preparation

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 8 December 2011

been collected and the sample is removed from the column. [Note

Table 1: Sample Characterization and Appropriate Methods

: Additional 

parameters may be measured if required or requested by the data user.]

(Note

Characteristic

: Any approved ASTM, USGS, EPA, Association of Official Analytical 

Chemists (AOAC), or Standard Methods analytical method may be 

used for sample characterization)

Method

Neutralization Potential Sobek, 1978 (EPA-600/2-78-054); Skousen et al. 1997

Total Sulfur 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) Percent of Sample (by weight)

3/8" to 4 40

4 - 10 25

10 - 16 15

16 - 35 10

35 - 60 5

Less than 60 5

Total 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

8.3

: The total weight of the sample added to the column must be recorded to the 

nearest 1.0 gram, for use in results calculations.

8.3.1 Maintain the column at a temperature between 20 - 25°C  3°C 

(e.g., 22°C  3°C).

Column Maintenance
EPA Method 1627 9 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

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). 

 – 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.

Note

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). 

: 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. 

8.4.3 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 10 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

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. 

Collection and Analysis

Note

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. 

: 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).

8.5.1.2 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 μm 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 11 December 2011

Table 3: Analytes and Appropriate Methods

Note

Analyte

: Any approved ASTM, USGS, EPA, AOAC, or Standard Methods analytical 

method may be used for leachate analysis

Method

pH EPA 150.1; Std. Methods 4500-H; ASTM D1293; 

USGS I-1586

Dissolved Metals ** 

(e.g., Fe, Mn, Al, Mg, Ca, Se)

EPA 200.7, 236.1, 236.2; Std. Method 3111, 3113, 3120; 

ASTM D1068; USGS I-3381

Sulfate EPA 375.1, 375.2, 375.4; Std. Methods 4500

Alkalinity (to pH 4.5) EPA 310.1, 310.2; Std. Methods 2320B; 

ASTM D1067; USGS I-1030, I-2030

Acidity / Net Acidity (to pH 8.2) EPA 305.1; Std. Methods 2310; ASTM D1067 

Specific Conductance EPA 120.1; Std. Methods 2510B; ASTM D1125; USGS 

I-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

9.3

­ 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.

Duplicate Samples

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. 

 – 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.

9.3.2 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

%100*

2/)21(

21

CC

CC

RPD

+

− =

Where

C1 = concentration in primary sample 

: 

C2 = concentration in duplicate sample 
EPA Method 1627 12 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 

 (Leachate Volume Out L) L

mg Analyte, mg  × , 

 



 =

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 13 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 14-week 

RPD

Initial Flush 

RPD

Weathering Test RPD 

(Difference between 14-week and initial flush RPD)

Fe 90.4 50.9 39.5

Mn 52.5 44.1 8.4

Al 72.5 38.6 33.9

Ca 21.9 38.8 (16.9) *

Mg 21.4 16.4 5.0

Se 42.9 26.2 16.7

Zn 60.2 52.0 8.2

Na 25.1 21.1 4.0

K 23.7 21.5 2.2

SO4 27.5 20.4 7.1

Alkalinity 28.7 35.2 (6.5) *

Acidity 99.9 27.0 72.0

Conductivity 13.2 11.1 2.1

Mean absolute difference

pH 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 14 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

12.3 Brady, K.B.C., R.J. Hornberger, B.E. Scheetz, and C.M. Loop. Refinement of ADTI-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.

, Chapter 6: Overburden Sampling Considerations. December 2000. 

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

12.6 Griffiths, J.C. 

, Chapter 5: Guidelines and 

Recommendations for Use of Kinetic Tests for Coal Mining (AMD) Prediction in the Eastern 

United States. December 2000. 

Scientific Method in Analysis of Sediments

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. 

, New York: McGraw Hill Book Co. 

1967. 

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, 

12.11 Langmuir, D. Aqueous Environmental Geochemistry, Upper Saddle River, New Jersey. Prentice 

Hall, Inc. pp. 600. 1997 

Chapter 7 - Kinetic 

(Leaching) Tests for the Prediction of Mine Drainage Quality, October 1998 

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

Press. pp. 811. 1998 
EPA Method 1627 15 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.1, 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

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. 

, June 1, 

1998. 

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

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. 

, Pennsylvania Department of 

Environmental Protection, 1998. 

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 of Interlaboratory 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.F., 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 16 December 2011

13.0 Forms and Figures 

Form 1

Example Daily Monitoring Reporting Form

: 

Sample ID:

Column 1 Column 2

Date / 

Time

Temp.

oC

Flow 

(Lpm)

% CO2 

(in exhaust)

Flow 

(Lpm)

% CO2 

(in exhaust)

Notes

Form 2

Example Weekly Monitoring Reporting Form

: 

Sample ID:

Date / 

Time Week #

Water In

(mLs)

Water Out

(mLs) pH

Conductivity

(μmhos/cm)

Alkalinity

(to pH 4.5)

mg/L as CaCO3

Acidity

(to pH 8.2)

mg/L as CaCO3

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-10

Week-10
EPA Method 1627 17 December 2011

Figure 1: Leaching Column
EPA Method 1627 18 December 2011

Figure 2: Humidified Air/Gas
EPA Method 16271 A-1 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-1). 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 NP Skousen %S

96.97 49.68 0.59

96.96 49.31 0.59

96.98 47.61 0.56

96.97 47.07 0.59

Avg 96.97 Avg 48.42 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

Using the Average NP number (Table A-1) 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: 

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

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 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: 

. The “Cation” Approach 

(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 16272 A-2 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, Xray 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. 

(Leachate Volume Out L) L

mg Analyte, mg  × , 

 



 =

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 CaCO3 from Ca 

( ) L mg Ca

L

mg  × = 1.49279.00.176 

 





 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. 

 and 

3 mg Ca =× 8.1225.21.49 mg CaCOas

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

Calculating CaCO3 from Mg

( ) L mg Mg L

mg  × = 2.23279.01.83 

 





 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. 

 and 

3 2.23 mg Mg =× 0.951.4 mg CaCOas
EPA Method 16273 A-3 December 2011

Calculating CaCO3 from Ca + Mg

3 8.122 mg Ca + 0.95 mg Mg = 8.217 mg CaCOas

 The next step is to simply combine the calcium carbonate equivalents 

calculated above:

Therefore, during the course of the previous week, 217.8 mg of carbonates, measured as CaCO3

equivalent, were dissolved. 

Step 2b

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. 

. The “Anion” Approach 

• 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. 

( ) 3 520 279.0 L 1.145 mg CaCO

L

mg  × = 

 





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 SO4

2- + 4 H+

For every mole of pyrite oxidized there are 2 moles of sulfate produced and 4 moles of H+

. It takes 2 

moles of CaCO3 to neutralize 4 H+

. This relationship can be written as:

4 mol H+__ 

= 2 mol CaCO3 = 

2 mol SO4

2- 2 mol SO42- 192 g SO42-

200 g CaCO3

Therefore, for every 1 mg/L (or gram) of sulfate, 1.04 mg/L (or gram) of acidity, as CaCO3, are produced. 
EPA Method 16274 A-4 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:

( ) 3 L 5.86279.004.1298 mg neutralized alkalinity CaCOas

L

mg  × = 

 



 ×

Calculating CaCO3 from Alkalinity + Sulfate

3 3 1.141 mg Alkalinity CaCO + 5.86 mg neutralized alkalinity = 6.227 mg CaCOas

 The next step is to simply combine the calcium carbonate 

equivalents calculated above:

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: 

CaCO weathered

g

g %25.0100 3 91 0.

2276.0

=×















Step 2 c. Compare the two methods. Figure A-1 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 16275 A-5 December 2011

0 5 10 15 20 25 30

% CaCO3 from Ca + Mg

0

5

10

15

20

25

30

35

40

% CaCO3 from HCO3 and SO

4-acidity

HCS-IN

LKFC-PA

KBF-WV

BCS-PA

MKSS-PA

Figure A-1. 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-1 was used for calculations. 

Step 1

Using the average percent sulfur value (Table A-1) 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: 

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

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 16276 A-6 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: 

L mg S weathered mg SOL 7.27279.0

3

/298 4 =×

To determine the percentage of the available sulfur that was weathered during this time period use the 

following equation: 

S weathered

g

g %25.0100

9.10

0277.0

=×















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 16277 A-7 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 2 3 4 5 6 7 8 9 10 11 12

Week

Vol

Out

mL

mg/L 

Ca mg Ca

Cumulative 

mg Ca

Cumulative 

mg Ca as 

CaCO3

mg/L 

Mg mg Mg

Cumulative 

mg Mg

Cumulative 

mg Mg as 

CaCO3

Cumulative 

Ca + Mg as 

CaCO3

% CaCO3 

weathered 

each week 

from 91.0 g

0 1356 99.8 135.33 135.33 338.32 57.1 91.83 91.8 377.90 716.22 0.79

1 310 270.0 83.70 219.03 547.57 148.0 54.41 146.24 601.82 1149.39 1.26

2 340 240.0 81.60 300.63 751.57 131.0 52.82 199.07 819.20 1570.77 1.73

3 295 186.0 54.87 355.50 888.75 93.3 32.64 231.71 953.53 1842.28 2.02

4 309 175.0 54.08 409.57 1023.93 82.7 30.31 262.02 1078.25 2102.19 2.31

5 270 170.0 45.90 455.47 1138.68 78.8 25.23 287.25 1182.09 2320.78 2.55

6 279 176.0 49.10 504.58 1261.44 83.7 27.70 314.95 1296.07 2557.51 2.81

7 296 147.0 43.51 548.09 1370.22 68.7 24.12 339.06 1395.32 2765.54 3.04

8 285 153.0 43.61 591.69 1479.24 68.4 23.12 362.18 1490.46 2969.70 3.26

9 285 163.0 46.46 638.15 1595.37 84.3 28.49 390.68 1607.72 3203.09 3.52

10 268 156.0 41.81 679.96 1699.89 68.6 21.80 412.48 1697.45 3397.34 3.73

11 260 142.0 36.92 716.88 1792.19 62.7 19.33 431.82 1777.01 3569.21 3.92

12 260 148.0 38.48 755.36 1888.39 59.8 18.44 450.26 1852.90 3741.29 4.11

13 274 162.0 44.39 799.75 1999.36 68.7 22.33 472.58 1944.77 3944.13 4.33

14 264 151.0 39.86 839.61 2099.02 66.4 20.79 493.37 2030.32 4129.35 4.54
EPA Method 16278 A-8 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). 

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

Week

50

100

150

200

250

300

Concentration (mg/L)

Calcium

Manganese

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

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

Week

0

40

80

120

160

Flux (load), mg of Analyte

Calcium

Manganese

Figure A-3. Flux (load) of analyte. 

Calcium

Magnesium

Calcium

Magnesium
EPA Method 16279 A-9 December 2011

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

Week

0

200

400

600

800

1000

Cumulative Flux (load), mg of Analyte

Calcium

Manganese

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

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

Week

0

1000

2000

3000

4000

5000

Cumulative Flux (load), mg as CaCO3

Calcium

Manganese

Ca + Mg

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).

Calcium

Magnesium
EPA Method 162710 A-10 December 2011

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

Week

0

1

2

3

4

5

Percentage of CaCO3 Weathered

Ca + Mg as CaCO3

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 162711 A-11 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 16271 B-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+ + SO4

2- + 2 H2O 

CaCO3 Ca2+ + CO3

2-

The chemical reaction can be formulated into a mathematical expression as follows:

[ ] [ ]

[ ] [ ] o

xw

zy

K

BA

DC = ××

Where: the brackets represent chemical activity in moles/L, and Ko 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 Ko 

at temperatures other than 25°C. 

At equilibrium, gypsum and calcite solubility are represented as:

[ ] [ ] [ ] o K

OHCaSO

OHSOCa = ×× + −

24

2

2

2

4

1 2

2* −≈ 58.4log o K

and 

[ ] [ ]

[ ] o K

CaCO

COCa = × + −

3

2

3

2

 −≈ 48.8log o K

The product of the left side of the above two equations is called an ion activity product (IAP), and is 

calculated using results of leachate analysis (see Section 8.5 of Method 1627). The IAP is compared to 

the equilibrium constant Ko to calculate a saturation index S.I. as follows: 

o K

IAP IS 10 = log..

Because the ion activities are expressed in moles per liter, it is mathematically convenient to calculate 

IS .. in log base 10. 

The computed saturation index S.I. is interpreted as follows: 
EPA Method 16272 B-2 December 2011

• S.I. less than zero(0), 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(0), 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(0) 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 Ko

 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: 

×= ∑ 2 5.0 ii I zm

Where: mi is molar concentration, and i 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. 

Az I i i

2 logγ −= (Debye-Huckel)

I

I

Az I i

i ×−

+

− = 3.0

1 log

2

γ (Davies)

Where: A is a constant, I is ionic strength, and γi is 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 γi as follows:

Activity Coefficient (γi ) = (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 16273 B-3 December 2011

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-1 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-1 for 12 weeks. 

Figure B-1. Calcite and Gypsum Saturation Indices, Sample BCS3-PA

Calcite and Gypsum Saturation Indices, Sample BCS3-PA

-2

-1.5

-1

-0.5

0

0.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Week

S.I.

Calcite

Gypsum
EPA Method 16274 B-4 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 (1)

Week pH Alkalinity Temperature Ca Mg Sulfate Na K Calcite 

S.I.

Gypsum 

S.I.

1 7.20 198.5 20.8 204 103.8 678 11.3 6.1 0.13 -0.65

2 7.24 222.7 21.8 121.5 68.6 392 6.9 6.5 0.09 -0.99

3 7.33 239.2 21.5 102.5 57.6 270 5.0 5.7 0.17 -1.17

4 7.32 229.1 22.4 99.2 53.8 203 2.8 4.4 0.16 -1.29

5 7.29 249.3 21.9 93.9 38.1 162 2.4 4.3 0.16 -1.37

6 7.34 220.5 21.5 81.4 33.2 135 1.4 4.3 0.11 -1.47

7 7.18 221.9 22 74.7 31.8 147 2.3 3.2 -0.08 -1.47

8 7.14 252 21.1 90.8 40.7 133 2.4 3.9 0.00 -1.46

9 7.23 230.9 20.4 77.8 33.6 110 1.7 3.9 -0.01 -1.57

10 7.18 264.9 21.9 103.4 44.7 137 1.7 3.5 0.12 -1.41

11 7.15 220.3 22 75.7 27 112 1.5 3.4 -0.09 -1.56

12 7.02 259.3 22.2 99.7 33.5 148 1.5 2.2 -0.06 -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.