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Article

Kinetic Column Evaluation of Potential Construction Options for Lessening Solute Mobility in Backfill Aquifers in Restored Coal Mine Pits, Powder River Basin, USA

by
Jeff B. Langman
* and
Julianna Martin
Department of Earth and Spatial Sciences, University of Idaho, Moscow, ID 83844, USA
*
Author to whom correspondence should be addressed.
Hydrology 2025, 12(1), 8; https://doi.org/10.3390/hydrology12010008
Submission received: 12 December 2024 / Revised: 4 January 2025 / Accepted: 6 January 2025 / Published: 7 January 2025
(This article belongs to the Topic Transport, Transformation and Cycling of Elements in Water and Soil and Their Response to Human Activities)
Browse Figures
Figure 1
<p>Location of the Cordero Rojo Mine in the Powder River Basin of Wyoming, USA.</p> "> Figure 2
<p>An example of the removal of overburden and waste generation during open-pit coal mining at the Cordero Rojo Mine, Powder River Basin, Wyoming, USA.</p> "> Figure 3
<p>Overburden formations and coal seam at the Cordero Rojo Mine, Powder River Basin, Wyoming, USA. The pit perspective and stepped wall distort the coal seam thickness (about 8 m) in relation to the overburden thickness (about 75 m).</p> "> Figure 4
<p>Sieving of Cordero Rojo Mine waste rock to ≤6.3 mm onsite.</p> "> Figure 5
<p>Kinetic columns for benchtop experiments conducted with Cordero Rojo Mine waste rock.</p> "> Figure 6
<p>Major and trace element composition of the Fort Union and Wasatch waste rock from the Cordero Rojo Mine. * Total Fe expressed as FeO.</p> "> Figure 7
<p>Field parameter results for (<b>a</b>) Eh, (<b>b</b>) specific conductance, (<b>c</b>) pH, and (<b>d</b>) alkalinity of leachate from the (1) unamended column, (2) zeolite-amended column, (3) soil-amended column, (4) compaction column, and (5) rinsed column.</p> "> Figure 8
<p>Anion concentrations for leachate from unamended, zeolite, soil, compacted, and rinsed waste rock columns for (<b>a</b>) chloride, (<b>b</b>) fluoride, (<b>c</b>) nitrate, and (<b>d</b>) sulfate.</p> "> Figure 9
<p>Arsenic concentrations for leachate from (<b>a</b>) zeolite, (<b>b</b>) soil, (<b>c</b>) compacted, and (<b>d</b>) rinsed waste rock columns. Non-detection values were set to half the reporting limit (0.5 μg/L).</p> "> Figure 10
<p>Cadmium concentrations in leachate from (<b>a</b>) zeolite, (<b>b</b>) soil, (<b>c</b>) compacted, and (<b>d</b>) rinsed waste rock columns for the first 18 days of the experiment. Non-detection values were set to half the reporting limit (0.5 μg/L).</p> "> Figure 11
<p>Iron concentrations for (<b>a</b>) zeolite, (<b>b</b>) soil, (<b>c</b>) compaction, and (<b>d</b>) rinsed amended columns. Non-detection values were set to half the reporting limit (5 μg/L).</p> "> Figure 12
<p>Mean particle size and ζ potential of leachate from the unamended, zeolite, soil, compacted, and rinsed waste rock columns for the first 55 days of the experiment.</p> ">
Versions Notes

Abstract

:
Following open-pit coal mining in the Powder River Basin, landscape reconstruction includes the construction of backfill aquifers from overburden waste rock. With overburden disaggregation and the re-introduction of groundwater, the weathering of newly available mineral surfaces and mobilization of nanomaterials can impact groundwater quality even when such issues were not previously detected in the overburden’s groundwater. Kinetic columns of Powder River Basin waste rock were used to evaluate backfill construction options—zeolite amendment, and soil amendment, compaction, rinse—that could reduce potential groundwater quality impacts. The leachate from each column was collected twice weekly for 20 weeks. The Eh and pH of the leachate substantially varied during an initial high-weathering period indicative of the traditional weathering of newly exposed mineral surfaces and the weathering and flushing of mobile particles. Correspondingly, select elements, such as arsenic and cadmium, were present in relatively high concentrations during this initial weathering period. Waste rock that was compacted or rinsed produced leachate with less solutes and potential contaminants when compared to the unaltered and zeolite- and soil-amended waste rock. Greater compaction during backfilling is possible but may require additional consideration for connecting the surface drainage network to the surrounding area. Rinsing of the waste rock is a viable construction option because of the temporary storage of the waste rock prior to backfilling but would require leachate collection for contaminant treatment.

1. Introduction

A backfill aquifer is produced from the filling of a mine pit with waste rock (e.g., mined overburden) and the return of groundwater from infiltrating precipitation and lateral inflow from the surrounding aquifer(s). The mining (blasting and transport) of the waste rock produces a new aquifer matrix with the generation of new mineral surfaces and nanomaterials that can produce high weathering and solute transport rates [1,2,3,4,5,6,7,8,9]. The evolution of waste rock weathering is visible in the temporal change in solute release with an initial peak in concentrations until a new equilibrium of weathering is established [4,9,10,11,12,13]. The difficulty in understanding potential water quality issues in backfill aquifers is our limited ability to predict the availability of potential contaminant sources contributing to solute release in these modified matrices. Such issues are part of the global issue of mine waste disposal where there may be a perception of a non-hazardous mine waste that can still be a source of groundwater contamination [14,15,16]. Therefore, the characterization of waste rock and potential solutes is necessary for proper landscape reconstruction and closure planning to limit potential contamination [17,18]. The purpose of this study was to use benchtop kinetic columns to test potential options for construction of backfill aquifers, which could minimize contaminant transport from newly available sources in the waste rock that were previously identified and described by Langman [19] and Martin and Langman [12] for waste rock from the Cordero Rojo Mine in the Powder River Basin, Wyoming, USA.
Backfill aquifers in the Powder River Basin (PRB), the largest coal mining district in the United States (Figure 1), have shown variable water quality and exceedance of water quality criteria for backfill aquifers when it was predicted that weathering of the waste rock would not result in groundwater contamination issues [2,6,20,21]. The semiarid climate of the PRB (annual precipitation average of 44 cm at Gillette, Wyoming (Figure 1) (Western Regional Climate Center)) and its low topographic relief (300 m total relief across the basin with a local relief typically <100 m [22]) allow for limited precipitation infiltration and a stream network that consists of ephemeral, intermittent, and perennial streams [23]. Reclamation of coal mines in the PRB has produced a range of water quality issues in backfill aquifers, which have not been attributed to any particular waste rock characteristic or reclamation process [24,25,26]. As part of a larger research project, a kinetic column experiment was conducted to evaluate the environmental conditions and solutes produced with the weathering of fresh waste rock from the Cordero Rojo Mine in the PRB (Figure 1). Martin and Langman [12] found the waste rock produced a leachate that substantially varied in Eh and pH during the first 55 days, which corresponded to a period of high specific conductance (>1000 µS/cm) and alkalinity (>200 mg/L). Correspondingly, anion and cation concentrations were the largest during this early weathering period, and filter fractions indicated multiple forms of transported elements. After this early weathering period, column leachate evolved towards a weathering equilibrium of neutral, oxidizing, and low-solute conditions. This evolution was reflected in the decline and stabilization or non-detection of metal(loid) concentrations reflective of a shift to primarily bulk aluminosilicate weathering [12].
Overall, the mining of the overburden formations and use of the waste rock for backfill aquifers create newly available mineral surfaces and nanomaterials that will weather to produce solute concentrations not typically found in groundwater associated with the original overburden. Langman [19] found that predictive modeling of such newly available contaminant sources is difficult without waste rock and solute characterization. With such difficulty in understanding potential water quality impacts from newly available contaminant sources in such waste rock, the final part of the larger research project was to examine readily available construction options for landscape reconstruction (e.g., backfill aquifer construction) that could reduce impacts on groundwater quality. The results of this current study on backfill aquifer construction options build on the results published by Martin and Langman [12] and Langman [19] that described the new contaminant issue and difficulty in estimating the potential release of the contaminants with landscape reconstruction.

1.1. Powder River Basin Geology and Coal Mining

The PRB of Montana and Wyoming (Figure 1) is a north–northwest-to-south–southeast-trending asymmetric syncline. The basin contains >5500 m of sediments along the basin axis (Figure 1) that sit atop Precambrian igneous and metamorphic rocks dipping gently westward from the Black Hills [27]. The structural axis is located along the western part of the basin with the western limb characterized by steeply dipping (~20°) strata and the eastern limb characterized by gently dipping (2–5°) strata, including the Cretaceous and Tertiary coal-bearing rocks [28]. Because the coal beds are thick, shallow, and gently dipping along the eastern margin, large open-pit mines have been developed in this area (e.g., Gillette Coal Field (Figure 1)) to extract coal. A typical mining operation of this region consists of overburden and coal removal with corresponding backfill (Figure 2) moving westward [28]. Collection of waste rock for this study occurred at the Cordero Rojo Mine, which annually produces 9 to 14 million tonnes of coal as part of the 200 million tonnes annually produced in the PRB [29].
The PRB waste rock is derived from an overburden sequence of interbedded fluvial, lacustrine, and palustrine deposits (Figure 3) consisting of the Wasatch and Fort Union formations [30,31,32]. The heterogeneity of the sedimentary formations allows for a range of groundwater travel times with hydraulic conductivities ranging from 73 to 240 cm/d for the overburden formations within the Gillette Coal Field [33]. These formations contain an abundance of sandstone with some limestone and relatively non-sulfidic mudstones [34] whose paleoenvironments produced the low sulfur coal [35,36,37]. The PRB coal contains accessory minerals such as arsenic-bearing pyrite [FeS2] and cadmium-bearing sphalerite [(Zn,Fe)S] [38]. Primary contaminants (exceedance of water quality criteria) detected in the PRB backfill aquifers include arsenic [As], cadmium [Cd], manganese [Mn], and selenium [Se] [39]. Such contaminates are typically not found in groundwater that has interacted with the Wasatch and Fort Union formations [40]. Earlier studies conducted as part of this research project indicated that As and Fe were associated with small coal particles and potentially nanopyrite, while Cd and Se were associated with salts, such as gypsum [CaSO4], that likely formed with the weathering of the coal (e.g., sulfur/sulfide oxidation) and subsequent mineral precipitation [12,19].

1.2. Construction Options for Reducing Contaminant Mobility

To evaluate potential construction options for reducing contaminant mobility in waste rock from coal mining in the PRB, two waste rock amendments (zeolite and soil) were selected to evaluate potential additives that could reduce contaminant mobility through chemical processes and two landscape reconstruction modifications (compaction and flushing/rinsing) were selected to evaluate potential physical processes for minimizing the interaction of contaminants and infiltrating water. Amendments to backfill are not common for non-acid-generating waste rock, but potentially low-cost and readily available amendments, such as zeolite or collected soil (overburden), may provide sufficient reactive surfaces for the capture or retardation of newly available contaminants. An advantage of using zeolite [hydrated (Na,K,Ca)2-6AlxSiyOz] as an amendment is the microporous and sorbing nature of these aluminosilicate grains that makes them useful in water treatment systems [41,42,43,44,45]. Zeolites have the capacity to sorb charged solutes into and on their micropore structure [43,46,47,48,49]. Soil covers are a common part of mine site restoration, and existing soils are often collected and stored onsite for post-mining restoration [50]. A soil has the capacity to improve water quality through pH buffering and adsorption/exchange processes because of its organic, mineral, and microbial components [51,52]. Compaction of waste rock decreases subsidence/settling and is an important stabilizing process during construction of backfill aquifers, and the amount of compaction can influence the aquifer’s porosity/permeability and hydraulic pathways [53,54,55,56,57,58]. The flushing/rinsing modification could be implemented if backfilling is delayed, exposing the waste rock to longer surface weathering.

2. Materials and Methods

To evaluate the mobilization of contaminants and potential construction options that could be implemented to minimize contaminant release and/or mobility, waste rock from the Cordero Rojo Mine was placed in five kinetic columns under warm-room (20 °C) conditions and exposed to a semiweekly saturation and leachate collection cycle for 20 weeks. The kinetic columns consisted of unamended waste rock (control), waste rock amended with 5% zeolite, waste rock amended with 5% soil, waste rock compacted to 90% of the loose-fill volume, and pre-rinsed waste rock. The addition of an inorganic amendment for groundwater remediation is dependent on site-specific factors, but such additives commonly compose 5 to 30% per volume of the media [59]. The lowest possible additive percent was considered for the zeolite and soil amendments to minimize potential costs of such remediation actions.

2.1. Waste Rock Sampling and Analysis

Waste rock samples of the Wasatch and Fort Union formations were collected within two weeks of initial excavation from the Cordero Rojo Mine (nearest waste piles to the active mining area). The waste rock were collected using the “clean hands” techniques as described for field and laboratory experiments involving trace metals [60,61]. The Wasatch and Fort Union waste rock were segregated during mining (two blast and excavation steps for overburden removal) and were separately collected and screened to ≤6.3 mm (Figure 4) using a random selection method per the standard practice for sampling aggregates [62,63,64,65,66]. The sample collection included 86 kg of Wasatch waste rock and 214 kg of Fort Union waste rock that align with the 20/80% distribution of waste-rock types (Wasatch/Fort Union). The screened samples were sealed in 0.02 m3 buckets, transported to the University of Idaho, and stored at 5 °C before drying at 125 °C for 48 h.
Pre-experiment and post-experiment waste rock were analyzed for grain size distribution and slake durability [67] at the University of Idaho. Wasatch and Fort Union waste rock were evaluated for major- and minor-element concentrations by X-ray fluorescence (XRF) at the GeoAnalytical Laboratory (fused beads and an Advant’XP+ sequential XRF) at Washington State University. Additionally, samples of Fort Union and Wasatch waste rock were examined using a Zeiss Supra 35 Variable-Pressure FEG scanning electron microscope with Noran System Six EDS at the University of Idaho Electron Microscopy Center to evaluate potential contaminant sources derived from the mining process, which is described in Langman [19].

2.2. Kinetic Column Construction

The kinetic columns consisted of clear PVC, 0.6 m in length and 0.1 m in diameter (Figure 5). Each column was sealed with rounded endcaps, and a drip system was attached to the upper cap for the introduction of deionized water. The top cap contained a 0.5-cm hole to allow air to escape during water introduction. A two-layered mesh filter was placed at the bottom of each endcap for the retention of the waste rock material. The mesh filter contained sufficiently large diameter openings to allow ≤10 µm particles into the upper mesh and restrict ≥4 µm particles from moving through the lower mesh prior to discharge through 1-cm tubing into leachate collection containers. The goal of the mesh filter was to allow solutes in the leachate to pass to the collection system, similar to the transport or restriction of solutes (micron to nanometer in scale) in a backfill aquifer. Additionally, the mesh filters needed to remain open (no clogging) during the entire experiment period (20 weeks).
The waste rock generated onsite from the mining of the overburden is composed of about 20% Wasatch Formation rock and 80% Fort Union Formation rock. Therefore, each column was loaded with 0.8 kg of Wasatch waste rock and 3.2 kg Fort Union waste rock to represent the overburden distribution, which is replicated with backfill aquifer construction. For the zeolite and soil amendments, the amendment was homogenized with the Fort Union waste rock by the roll method [66]. The Fort Union Formation is known to contain greater concentrations of potential contaminants compared to the Wasatch Formation [12], and the Fort Union Formation overlies the coal seams, such that minor amounts of coal (and potential contaminants) are incorporated into the Fort Union waste rock. Therefore, an amendment application in a backfill aquifer would likely target water passing through the Fort Union waste rock. A specific zeolite mineral, clinoptilolite [(Na,K,Ca)2-3Al3(Al,Si)2Si13O36·12H2O] was obtained from KMI Zeolite, Inc. (Amargosa Valley, NV, USA), which had a diameter range of 2.4 to 4.8 mm (4 × 8 mesh, median of 3.5 mm) and an approximate surface area of 40 m2/g (manufacturer-determined). This type of zeolite has a 10- and 8-ring micropore structure, which is considered a larger ring size in the zeolite family [68]. To reduce the possible influence on solute chemistry from nanomaterials sorbed to the zeolite that were generated during mining, clinoptilolite grains were triple-rinsed with deionized water and dried at 80 °C. The soil amendment was collected from the soil repository at the Cordero Rojo Mine and was unaltered prior to homogenization with the Fort Union waste rock. The compacted column consisted of 4 kg of waste rock compacted to 90% of a loose pour volume through agitation and a hydraulic press. The rinsed waste rock was double-rinsed with deionized water prior to the insertion into the column.

2.3. Weathering Procedures and Leachate Analysis

The weathering cycle for each kinetic column consisted of the drip introduction of 1 L of deionized water and full saturation of the waste rock for 72 h followed by a 2 h drain period and a 6 h unsaturated period before re-saturation of the column, which was repeated for the 20-week experiment period (modification of the standard humidity cell protocol [64]) to simulate saturated conditions and allow for a sufficient leachate volume for analysis. The leachate from each column was analyzed for pH (±0.01 pH), Eh (±0.2 mV), and specific conductance (±0.01 µS/cm) with calibrated Orion 3-Star meters/probes. Alkalinity (±0.1 mg/L as CaCO3) was determined by an OrionStarT940 auto-titrator using 0.1 N HCl. Anion (bromide [Br], chloride [Cl], fluoride [Fl], nitrate–nitrite as nitrogen [NO3-NO2 as N] (nitrate or NO3), ortho-phosphate [PO4], and sulfate [SO4]) concentrations were determined by ion chromatography (Dionex Aquion Ion Chromatograph) from 0.45-μm filtered leachate. Cation (aluminum [Al], arsenic [As], barium [Ba], boron [B], cadmium [Cd], calcium [Ca], chromium [Cr], copper [Cu], iron [Fe], lead [Pb], magnesium [Mg], manganese [Mn], molybdenum [Mo], nickel [Ni], potassium [K], selenium [Se], sodium [Na], and zinc [Zn]) concentrations of unfiltered and filtered (0.45-μm and 0.2-μm filtered) leachate were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) for larger concentrations (Perkin Elmer Optima 8300 ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) for smaller concentrations (Agilent 7800 ICP-MS) at the University of Idaho Analytical Services Laboratory (all column leachate data are available in the provided Supplemental Materials).
Immediately after leachate collection, unfiltered leachate was measured for particle size distribution and ζ potential using a Brookhaven NanoBrook ZetaPALS. Samples were analyzed by dynamic light scattering for particle size distribution in water at 25 °C with a viscosity of 0.89 cP, a refractive index of 1.33, a scattering angle of 90°, a dielectric constant of 78.54, a laser wavelength of 659 nm, and inputted pH and conductivity values. Analysis of ζ potential was performed by laser Doppler electrophoresis (phase analysis light scattering). The laser beam passed through the sample undergoing electrophoresis, and the scattered light from the moving particles was frequency-shifted, from which the electrophoretic mobility (m2 V−1 s−1), U, was determined given the laser wavelength and the scattering angle. The ζ potential was calculated from the electrophoretic mobility using the Smoluchowski solution (ζ = μU/ε), where ε is the electric permittivity of the solution (C2 N−1 m−2) [69].
For comparative analysis, the leachate results are presented as temporal trends to evaluate differences in analyte evolution from the high-weathering period to the end of the kinetic column experiment. Select analytes are presented that represent primary environmental conditions (e.g., pH) and primary solutes of concern, such as As. Many of the analytes (Al, Ba, B, Cr, Cu, Pb, Ni, P, Na, and Zn) had results with >50 % non-detection and/or are unlikely contaminants within the PRB waste rock and were excluded from the results presentation. To supplement the temporal trend presentation of the analyte results, a Kruskal–Wallis test was performed for comparison of the column results to evaluate statistically significant differences between analyte distributions for each column. The Kruskal–Wallis test (analogous to a one-way ANOVA) is a non-parametric test for evaluating whether samples originate from the same distribution through an examination of differences between rank sums of the groups. For analyzing the analyte differences between the columns, the post hoc Dunn’s test with Bonferroni correction was used to identify stochastic dominance. The results of the statistical tests are discussed in the text, and all the statistical results (Χ2, p-values, and Dunn pairs) are presented in Appendix A.

3. Results

3.1. Physical and Chemical Characterization of Collected Waste Rock

Pre-experiment Fort Union waste rock had a greater percentage of fine (<0.15 mm) grains indicative of its low-energy depositional environment, as well as the presence of coarse (>2 mm) coal grains [12]. Comparatively, pre-experiment Wasatch Formation waste rock had a greater amount of 0.3 mm to 1 mm grains (e.g., sand) compared to the Fort Union waste rock. X-ray fluorescence (XRF) analysis indicated large concentrations of Al and silicon [Si] in the Wasatch and Fort Union waste rock (Figure 6) reflective of the dominant aluminosilicate minerals that compose these fluvial and lacustrine deposits [27,70,71]. Larger concentrations of redox-sensitive elements of As, Fe, Mn, and P were present in the Fort Union waste rock because of the low-energy depositional environments associated with this formation [72,73]. Correspondingly, the Fort Union sample had a greater surface area of 14.2 m2/g compared to the 5.1 m2/g for the Wasatch sample. The zeolite and soil amendments had similarly large surface areas at 12.9 m2/g and 10.1 m2/g, respectively. Given the greater presence of clays and coal particles in the Fort Union waste rock, potential contaminants, such as As and Se, were found in greater concentrations in the Fort Union waste rock, with As associated with coal particles and Se associated with higher clay content and was likely present as a salt (e.g., Se-bearing gypsum) [19].

3.2. Column Leachate Environment Condition Distributions and Trends

The environmental conditions for leachate from the unamended waste rock column indicated high variability during the first 55 days of the experiment (Figure 7). Leachate Eh fluctuated between negative and positive values, suggesting alternating oxidizing and reducing conditions with the greatest variability during the first 45 days (Figure 7a). The specific conductance of leachate from all columns, except the soil column leachate, decreased sharply during the first 40 days of the experiment, and pH remained near neutral for the entire experiment with the unamended column leachate having the lowest pH throughout the experiment (Figure 7b,c). Eh trends for amended/modified and unamended leachate were similar throughout the experiment (Kruskal–Wallis test p-value of 0.62, Appendix A) while pH, specific conductance, and alkalinity results indicated differences between the columns (p-value < 0.01). The zeolite-amended column released leachate with the highest pH and alkalinity throughout the experiment (Figure 7d), likely because of the release of hydroxyl groups (S-OH) associated with the (Si,Al)O4 tetrahedra of the zeolite as solutes undergo sorption/desorption [74]. The soil-amended leachate displayed a period of high specific conductance from day 23 until Day 90 (Figure 7b), diverging from the specific conductance trends observed in the other columns and indicating a potentially longer duration of solute flushing (e.g., nanomaterials) likely contributed by the soil amendment. The compacted column leachate had similar alkalinity and specific conductance distributions (no pairwise difference, Appendix A) and trends as the unamended leachate but exhibited a higher pH trend throughout the experiment compared to the unamended leachate (Figure 7c). The rinsed column leachate had the lowest alkalinity and specific conductance values and a pH trend similar to the compacted column leachate (no pairwise difference, Appendix A) (Figure 7).

3.3. Column Leachate Solute Distributions and Trends

3.3.1. Anions

Anion concentrations for the column leachates indicated relatively quick declines in concentrations following the initial flushing/weathering of the waste rock for all amendment/modifications (Figure 8). The statistical analysis of the anion concentrations indicated no difference between leachates for Cl (p-value = 0.43) and a difference between the leachates for F, NO3, and SO4 (p-value ≤ 0.01) with mixed pairwise differences for these anions (Appendix A). Leachate from the soil-amended column had the highest peak concentrations of Cl, F, and NO3 (Figure 8). Leachate from the compacted column and the rinsed column had similar peak concentrations of Cl and SO4 that were lower than concentrations in leachate from the remaining columns. All amended/modified column leachate contained higher peak concentrations of F compared to the unamended column leachate (Figure 8b). Leachate from the soil- and zeolite-amended columns contained the largest peak Cl concentrations—29 mg/L and 25 mg/L, respectively—compared to the unamended column peak concentrations of 22 mg/L. Leachate from the compacted and rinsed columns had the lowest peak concentrations of Cl at 16 mg/L and 17 mg/L, respectively. Peak NO3 concentrations in leachate from the unamended, zeolite, and compacted columns were similar at approximately 17 mg/L with the rinsed column leachate containing a peak concentration of 12 mg/L, and the soil-amended leachate had a peak concentration of 37 mg/L (Figure 8c). All column leachate indicated SO4 peak concentrations of >44,000 mg/L except for leachate from the zeolite-amended column where SO4 concentrations peaked at 3900 mg/L.

3.3.2. Metal(loid)s

Metal(loid) concentrations in the leachate from the amended/modified columns varied according to the source (e.g., pyrite oxidation vs. salt dissolution) and amendment or modification. A waste rock metal(loid) source discussion is present in Martin and Langman [12] and Langman [19]. Arsenic concentrations for leachate from the zeolite-amended column (Figure 9a) had consistently larger values (largest rank distribution, Appendix A) compared to leachate from the other columns (Figure 9), which are the result of the greater presence of As in the zeolite amendment (Figure 6). The double-peak trend of As release in the leachate for the amended/modified columns occurred in all unfiltered and filtered As trends except for the rinsed waste rock column. This double-peak trend also was observed with the unamended column leachate [19]. The leachate from the soil-amended column (Figure 9b) indicated a greater divergence between unfiltered and filtered concentrations (decreased rank distribution for filtered concentrations, Appendix A), indicating a particle source that was released from the column with continued flushing. Both compacted and rinsed columns (Figure 9c,d) had lower As concentrations compared to the unamended leachate, as well as reduced peaks and relatively consistent post-peak concentrations compared to the unamended column leachate (Figure 9).
Although Cd concentrations quickly decreased to non-detect levels after the first week (no statistical analysis because of the large majority of non-detections), this analyte has been found in salt byproducts from coal weathering and represent a potential contaminant source with liberation from mining of the overburden [75]. Cadmium concentrations in leachate from amended/modified columns indicated a similar trend to the unamended leachate [12], which consisted of an initial peak followed by a quick decline below reporting limits likely from salt dissolution and/or particle transport (Figure 10). However, zeolite and soil amendments produced lower Cd concentrations, and zeolite and compacted column leachate indicated no difference between unfiltered and filtered Cd concentrations (Figure 10a,b). Compacted and rinsed column leachate contained a similar peak value to the unamended column value of 1.4 μg/L, and the rinsed column leachate indicated the only divergence of unfiltered and both filtered Cd concentrations (Figure 10d).
The statistical analysis of Fe concentration distributions indicated the largest variability between unfiltered and filtered samples compared to other metal(loid)s (Appendix A, change in rank values and Dunn results between unfiltered and filtered). The zeolite filtered concentrations (0.45-μm and 0.2-μm filtered) were less than reporting limits by day 32, while the total (unfiltered) concentrations remained relatively high (Figure 11a), not following the unamended column leachate trend that displays equilibration as it nears the end of the experiment [12]. Leachate from the soil-amended column (Figure 11b) shows a slower increase and decrease compared to the other columns and displays a lower concentration peak. The compacted column (Figure 11c) had the highest Fe concentration (2200 μg/L) of the amended/modified column leachate on day 14, which resembles the Fe concentrations in the unamended column leachate [12]. The rinsed column leachate also shows a similar trend but equilibrates at a lower concentration with more filtered concentration variation (Figure 11d). None of the amended/modified column Fe trends contain an initial double Fe concentration peak that was detected in the unamended column leachate [12]. Unfiltered Fe concentrations diverge from filtered concentrations at various times and magnitudes in all amended/modified column leachate (Figure 11). The statistical analysis of the redox-sensitive elements Mn and Mo (Appendix A) indicate similar distributions and pairwise relations that were different than the Fe distributions and trends, which suggest that Fe has multiple source/transport forms compared to these other redox-sensitive elements.

3.4. Particle Size and Zeta Potential

The release of solutes from the waste rock in the kinetic column experiment exhibited typical solute trends for the weathering of fresh waste rock indicated by the specific conductance trends of a quick and early peak followed by a decreasing trend and a final stage of apparent steady-state weathering (Figure 7b). The expected early weathering peak contains readily available solutes (e.g., desorption or salt dissolution) as indicated by the filtered fractions of the metal(loid) concentrations (Figure 9, Figure 10 and Figure 11). The remaining fraction of the early peak solutes consist of larger particles that were transported through the columns as indicated by the mean particle diameter results (Figure 12). The unamended and compacted column leachates contained the largest particles (mean size > 2000 nm) during the early flushing period with the compacted leachate containing the smallest particles from day 25 to 55 period and the greatest rank difference for the entire distribution (Appendix A). Although rinsing the waste rock reduced the large particle flushing at the start of the experiment (Figure 12), the rinsed column leachate contained the largest solute particles from day 20 to 55 and overall largest rank (Appendix A). The zeolite and soil amendments decreased the large particle flushing at the start of the experiment, but each leachate contained similar particle sizes as the unamended leachate from day 25 to 55. The associated ζ potential values varied between negative and positive values during the first 55 days, reflective of the higher solute period where the greater reactivity of the mineral sources produced a range of cationic and anionic particles (Figure 12). The amendments and modifications to the waste rock did not have a substantial influence on ζ potential values (p-value < 0.01, Appendix A) where each column leachate produced similar ζ potential trends.

4. Discussion

The mining of the overburden formations creates newly available mineral surfaces and nanomaterials that weather to produce greater concentrations of potential contaminants not typically found in the regional groundwater contained in these formations. Mine waste commonly is evaluated for reactivity capacity (e.g., sulfide weathering) because of the potential for acidic rock drainage, but the liberation and availability of minerals and nanomaterials containing potential contaminants is an equally important concern that should be evaluated for waste rock disposal [76]. Contaminant mobilization with the weathering of waste rock is apparent in other coal mining regions around the globe, including the Canadian Elk River Valley [77], U.S. Appalachia [78], the Yanzhou Coal Field in China [79], and the coal mining areas of New South Wales in Australia [80]. The solute evolution with waste rock weathering is reflected in the decline and stabilization or non-detection of metal(loid) concentrations and specific conductance, reflective of a shift to primarily bulk aluminosilicate weathering when coal- and salt-associated elements—such as As and Cd—were not detected or at minimal concentrations. The results of the kinetic column experiment for the unamended waste rock [12,19] indicate a need to consider the release of contaminants into groundwater in backfill aquifers with landscape reconstruction. The four different waste rock amendments/modifications produced different influences on reducing solute/contaminant release because of their different chemical properties or physical characteristics.
The leachate results from the amended/modified columns indicate that compacted and rinsed modifications were able to reduce the release of solutes in comparison to the unamended waste rock and the waste rock containing soil and zeolite amendments. The compaction modification restricts the flow of water, thereby restricting weathering and solute release from the new contaminant sources (e.g., fresh mineral surfaces and nanomaterials) in the waste rock. Selection of the compaction option for landscape reconstruction would require greater heavy equipment use to further compact the backfill and provide a similar effect where the tested waste rock was subjected to a 10 % volume reduction compared to the unamended kinetic column (same mass of waste rock). The potential issue with greater compaction of the backfill during landscape reconstruction is a lower land surface, which still requires integration into the surrounding landscape that contains a surface-water network (e.g., small creeks). The surface topography of the compacted waste rock could be comparatively different from past reconstruction efforts by concentrating the lower topography to select areas, such as the formation of larger depressions/ponds that also could provide recharge to the aquifer. A smaller waste rock amount below these ponds because of the lower elevation would lessen the potential of groundwater contamination from the focused recharge.
Soil and zeolite amendments did reduce the concentrations of select solutes compared to the unamended column leachate, but these amendments did not consistently reduce the solute load of the leachate, particularly during the early weathering period, compared to the compacted or rinsed modifications of the waste rock. The rinse modification could comprise a flushing and collection of solutes prior to use of the waste rock in landscape reconstruction but would require a change in the temporary storage of the waste rock, including collection of leachate/runoff during storage. The potential period of additional surface exposure to precipitation and flushing of readily available solutes is unknown, but the rinsed modification constituted two cycles of full saturation and release of the rinse/leachate prior to start of the 20-week experiment. In the semi-arid climate of the PRB (e.g., limited precipitation and periods of high evaporation), such flushing/rinsing of the waste rock prior to its use in landscape reconstruction may not be possible unless reconstruction is delayed (governed by mine permit requirements). If such delays are possible, the waste rock would need to be placed on an impermeable barrier to allow for collection and treatment of leachate contaminants. Such an endeavor would be a substantially greater effort and cost incursion compared to the compaction option.

5. Conclusions

The restoration of open-pit mines may utilize waste rock for landscape reconstruction, which can include the construction of backfill aquifers. Waste rock weathering and contaminant transport may be different in backfill aquifers compared to the surrounding aquifer because of newly available mineral surfaces and transportable nano- to micro-scale particles generated during mining. The complexity of predicting the water quality of a backfill aquifer because of the alteration of the overburden to waste rock presents a challenge for mining companies who should consider reconstruction options/alternatives that may lessen the release of contaminants into groundwater. The exposure of waste rock from the Cordero Rojo open-pit coal mine in the Powder River Basin to kinetic column experiments produced expected leachate trends of early high solute release from reactive mineral surfaces and transportable nanomaterials followed by a relatively quick decline and a subsequent more gradual decline to an equilibrium trend based on aluminosilicate weathering. The length of the elevated contaminant concentrations during the pre-equilibrium period depends on the contaminant source and environmental condition, but the simple modification of greater compaction of the waste rock was able to have a substantive effect on solute concentrations by lessening the interaction of water with the fresh mineral surfaces and nanomaterials. Consideration for such a measure during landscape reconstruction could reduce water quality impacts and regulatory violations.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/hydrology12010008/s1, which contains all analytical results for the column leachates.

Author Contributions

Conceptualization, J.B.L.; methodology, J.B.L.; validation, J.B.L. and J.M.; formal analysis, J.B.L.; investigation, J.B.L. and J.M.; resources, J.B.L.; data curation, J.M.; writing—original draft preparation, J.B.L. and J.M.; writing—review and editing, J.B.L.; visualization, J.B.L. and J.M.; supervision, J.B.L.; project administration, J.B.L.; funding acquisition, J.B.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research received external funding from the U.S. Office of Surface Mining Reclamation and Enforcement under their Applied Science Program for Science and Technology Projects Related to Coal Mining and Reclamation (Grant# S21AC10037).

Data Availability Statement

All data analyzed as part of this study can be found in the attached Supplementary data file.

Acknowledgments

The authors want to thank the Office of Surface Mining Reclamation and Enforcement for their support and funding, Navajo Transitional Energy Company and Owen Tracy at the Cordero Rojo Mine for their collaboration, and the Geologic Society of America for their grant support for this project. The authors would also like to thank Gaige Swanson and Liam Knudson for their work on this project.

Conflicts of Interest

The authors declare no conflicts of interest.

Appendix A

Table A1. Results of the Kruskal–Wallis and Dunn tests for statistical analysis of the analyte data from the five leachate columns (unamended, zeolite amendment, soil amendment, compacted, and flushed/rinsed). A significant difference is indicated by the highlighted p-value and the presence of results from the Dunn test (Bonferroni corrected α = 0.005).
Table A1. Results of the Kruskal–Wallis and Dunn tests for statistical analysis of the analyte data from the five leachate columns (unamended, zeolite amendment, soil amendment, compacted, and flushed/rinsed). A significant difference is indicated by the highlighted p-value and the presence of results from the Dunn test (Bonferroni corrected α = 0.005).
AnalyteΧ2p-ValueUnamend (U)Zeolite (Z)Soil (S)Compact (C)Rinse (R)
Environmental Conditions (unfiltered):
Eh2.60.62921031089196
pH24.6<0.0171133999395
Dunn: U-Z, Z-C, Z-R
Sp. Cond.41.7<0.01851301297472
Dunn: U-Z, U-S, Z-C, Z-R, S-C, S-R
Alkalinity47.6<0.01871471097670
Dunn: U-Z, Z-S, Z-C, Z-R, S-R
Anions (0.45-µm filtered samples):
Cl3.80.438186717069
F53.2<0.0155981146050
Dunn: U-Z, U-S, Z-S, Z-R, S-C, S-R
NO319.5<0.018498557664
Dunn: Z-S, Z-R
SO421.7<0.0173861015661
Dunn: S-C, S-R
Metal(loid)s (unfiltered and 0.45-µm and 0.2-µm filtered samples):
As
Unfiltered45.8<0.01501001018245
Dunn: U-Z, U-S, U-C, Z-R, S-R, C-R
0.45 µm60.4<0.0147110968440
Dunn: U-Z, U-S, U-C, Z-R, S-R, C-R
0.2 µm62.3<0.0146112968440
Dunn: U-Z, U-S, U-C, Z-R, S-R, C-R
Fe
Unfiltered34.3<0.018389819034
Dunn: U-R, Z-R, S-R, C-R
0.45 µm43.9<0.019538899758
Dunn: U-Z, U-R, Z-S, Z-C, C-R
0.2 µm42.0<0.019641899556
Dunn: U-Z, U-R, Z-S, Z-C, S-R, C-R
Mn
Unfiltered39.2<0.0182371067677
Dunn: U-Z, Z-S, Z-C, Z-R
0.45 µm38.5<0.0181371067677
Dunn: U-Z, Z-S, Z-C, Z-R
0.2 µm38.4<0.0181371057678
Dunn: U-Z, Z-S, Z-C, Z-R
Mo
Unfiltered103<0.01401331015152
Dunn: U-Z, U-S, Z-S, Z-C, Z-R, S-C, S-R
0.45 µm102<0.01421341005150
Dunn: U-Z, U-S, Z-S, Z-C, Z-R, S-C, S-R
0.2 µm102<0.0141134995151
Dunn: U-Z, U-S, Z-S, Z-C, Z-R, S-C, S-R
Solution Particle Characteristics:
Particle size22.2<0.015960533681
Dunn: S-R, C-R
Ζ potential 0.695966526362

References

  1. Anderson, S.P.; Anderson, R.S.; Hinckley, E.-L.S.; Kelly, P.; Blum, A. Exploring Weathering and Regolith Transport Controls on Critical Zone Development with Models and Natural Experiments. Appl. Geochem. 2011, 26, S3–S5. [Google Scholar] [CrossRef]
  2. Bartos, T.T.; Ogle, K.M. Water Quality and Environmental Isotopic Analyses of Ground-Water Samples Collected from the Wasatch and Fort Union Formations in Areas of Coalbed Methane Development: Implications to Recharge and Ground-Water Flow, Eastern Powder River Basin, Wyoming; Water Resources Investigations Report; U.S. Geological Survey: Cheyenne, WY, USA, 2002.
  3. Colman, S.M. Rock-Weathering Rates as Functions of Time. Quat. Res. 1981, 15, 250–264. [Google Scholar] [CrossRef]
  4. Dosseto, A.; Turner, S.P.; Chappell, J. The Evolution of Weathering Profiles through Time: New Insights from Uranium-Series Isotopes. Earth Planet. Sci. Lett. 2008, 274, 359–371. [Google Scholar] [CrossRef]
  5. Drever, J.I.; Clow, D.W. Weathering Rates in Catchments. In Reviews in Mineralogy and Geochemistry; White, A.F., Brantley, S.L., Eds.; Mineralogical Society of America: Chantilly, VA, USA, 1995; Volume 31, pp. 463–483. [Google Scholar]
  6. Slagle, S.E.; Lewis, B.D.; Lee, R.W. Ground-Water Resources and Potential Hydrologic Effects of Surface Coal Mining in the Northern Powder River Basin, Southeastern Montana; Water Supply Paper 2239; U.S. Geological Survey: Reston, VA, USA, 1985. [CrossRef]
  7. St-Arnault, M.; Vriens, B.; Blaskovich, R.; Aranda, C.; Klein, B.; Ulrich Mayer, K.; Beckie, R.D. Geochemical and Mineralogical Assessment of Reactivity in a Full-Scale Heterogeneous Waste-Rock Pile. Miner. Eng. 2020, 145, 106089. [Google Scholar] [CrossRef]
  8. Sharma, V.K.; Filip, J.; Zboril, R.; Varma, R.S. Natural Inorganic Nanoparticles—Formation, Fate, and Toxicity in the Environment. Chem. Soc. Rev. 2015, 44, 8410–8423. [Google Scholar] [CrossRef]
  9. Acero, P.; Ayora, C.; Carrera, J.; Saaltink, M.W.; Olivella, S. Multiphase Flow and Reactive Transport Model in Vadose Tailings. Appl. Geochem. 2009, 24, 1238–1250. [Google Scholar] [CrossRef]
  10. Blowes, D.W.; Jambor, J.L. The Pore-Water Geochemistry and the Mineralogy of the Vadose Zone of Sulfide Tailings, Waite Amulet, Quebec, Canada. Appl. Geochem. 1990, 5, 327–346. [Google Scholar] [CrossRef]
  11. Yoo, K.; Mudd, S.M. Discrepancy between Mineral Residence Time and Soil Age: Implications for the Interpretation of Chemical Weathering Rates. Geology 2008, 36, 35–38. [Google Scholar] [CrossRef]
  12. Martin, J.; Langman, J.B. Leachate Experiments to Evaluate Weathering of Waste Rock for Backfill Aquifers in Restored Coal Mine Pits, Powder River Basin, USA. Geosciences 2024, 14, 4. [Google Scholar] [CrossRef]
  13. Langman, J.B.; Moore, M.L.; Ptacek, C.J.; Smith, L.; Sego, D.; Blowes, D.W. Diavik Waste Rock Project: Evolution of Mineral Weathering, Element Release, and Acid Generation and Neutralization during a Five-Year Humidity Cell Experiment. Minerals 2014, 4, 257–278. [Google Scholar] [CrossRef]
  14. Twardowska, I.; Stefaniak, S.; Szczepańska, J., VI. 6—High-Volume Mining Waste Disposal. In Waste Management Series; Twardowska, I., Ed.; Solid Waste: Assessment, Monitoring and Remediation; Elsevier: Amsterdam, The Netherlands, 2004; Volume 4, pp. 865–909. [Google Scholar]
  15. Nordstrom, D.K. Hydrogeochemical Processes Governing the Origin, Transport and Fate of Major and Trace Elements from Mine Wastes and Mineralized Rock to Surface Waters. Appl. Geochem. 2011, 26, 1777–1791. [Google Scholar] [CrossRef]
  16. Vriens, B.; Plante, B.; Seigneur, N.; Jamieson, H. Mine Waste Rock: Insights for Sustainable Hydrogeochemical Management. Minerals 2020, 10, 728. [Google Scholar] [CrossRef]
  17. McCullough, C.D.; Schultze, M.; Vandenberg, J.; Castendyk, D.; Fourie, A.B.; Tibbett, M.; Boggs, G. Mine Waste Disposal in Pit Lakes: A Good Practice Guide; Australian Centre for Geomechanics: Perth, Australia, 2024; pp. 1063–1076. [Google Scholar] [CrossRef]
  18. Ziemkiewicz, P.F.; Simmons, J.S.; Knox, A.S. The Mine Water Leaching Procedure: Evaluating the Environmental Risk of Backfilling Mines with Coal Ash. In Chemistry of Trace Elements in Fly Ash; Sajwan, K.S., Alva, A.K., Keefer, R.F., Eds.; Springer: Boston, MA, USA, 2003; pp. 75–90. ISBN 978-1-4757-4757-7. [Google Scholar]
  19. Langman, J.B. Kinetic Model Evaluation of Arsenic and Selenium Sources in Waste Rock of the Powder River Basin, USA. Mining 2024, 4, 469–488. [Google Scholar] [CrossRef]
  20. Hoy, R.; Ogle, K.; Taylor, M. Evaluation of Water Quality Conditions in Coal Mine Backfill in the Powder River Basin of Wyoming. J. Am. Soc. Min. Reclam. 2003, 2003, 427–447. [Google Scholar] [CrossRef]
  21. Ogle, K.M. Examination of Dissolved Concentrations of AS, B, Cd, Hg, Se, and Al in Water Quality from the Backfill Aquifer, Eastern Powder River Basin, Wyoming, 2005. In Proceedings of the 2007 National Meeting of the American Society of Mining and Reclamation, Gillette, WY, USA, 2–7 June 2007; pp. 561–580. [Google Scholar]
  22. Beikman, H.M. Geology of the Powder River Basin, Wyoming and Montana, with Reference to Subsurface Disposal of Radioactive Wastes; Open-File Report 62-7; United States Geological Survey: Reston, VA, USA, 1962; p. 84. [CrossRef]
  23. Rankl, J.G.; Lowry, M.E.; Geological Survey (U.S.). Ground-Water-Flow Systems in the Powder River Structural Basin, Wyoming and Montana; Water-Resources Investigations Report 85-4229; U.S. Geological Survey: Reston, VA, USA, 1990.
  24. Reddy, K.J.; Zhang, Z.; Vance, G.F. Selenite and Selenate Determination in Surface Coal Mine Backfill Ground Water. In Proceedings of the America Society of Mining and Reclamation, Gillette, WY, USA, 5–8 June 1995; pp. 237–245. [Google Scholar]
  25. Reed, S.M.; Singh, R.N. Groundwater Recovery Problems Associated with Opencast Mine Backfills in the United Kingdom. Int. J. Mine Water 1986, 5, 47–73. [Google Scholar] [CrossRef]
  26. Vance, G.F.; See, R.B.; Reddy, K.J. Selenite Sorption by Coal Mine Backfill Materials in the Presence of Organic Solutes. In Environmental Chemistry of Selenium; Frankenberger, W.T., Engberg, R.A., Eds.; Marcel Dekker, Inc.: New York, NY, USA, 1998; pp. 259–280. ISBN 978-0-429-07812-5. [Google Scholar]
  27. Dolton, G.L.; Fox, J.E.; Clayton, J.L. Petroleum Geology of the Powder River Basin, Wyoming and Montana; Open-File Report 88-450-P; U.S. Geological Survey: Reston, VA, USA, 1990. [CrossRef]
  28. Flores, R.M. Coalbed Methane in the Powder River Basin, Wyoming and Montana: An Assessment of the Tertiary-Upper Cretaceous Coalbed Methane Total Petroleum System; U.S. Geological Survey Digital Data Series DDS–69–C; U.S. Geological Survey: Reston, VA, USA, 2004; ISBN 0-607-98080-X.
  29. Wyoming State Geological Survey—Coal Production & Mining. Available online: https://main.wsgs.wyo.gov/energy/coal/coal-production-mining (accessed on 30 December 2024).
  30. Lorenz, J.C.; Nadon, G.C. Braided-River Deposits in A Muddy Depositional Setting: The Molina Member of the Wasatch Formation (Paleogene), West-Central Colorado, U.S.A. J. Sediment. Res. 2002, 72, 376–385. [Google Scholar] [CrossRef]
  31. Pocknall, D.T. Paleoenvironments and Age of the Wasatch Formation (Eocene), Powder River Basin, Wyoming. Palaios 1987, 2, 368–376. [Google Scholar] [CrossRef]
  32. Yuretich, R.F.; Hickey, L.J.; Gregson, B.P.; Hsia, Y.L. Lacustrine Deposits in the Paleocene Fort Union Formation, Northern Bighorn Basin, Montana. J. Sediment. Res. 1984, 54, 836–852. [Google Scholar] [CrossRef]
  33. Engle, M.A.; Bern, C.R.; Healy, R.W.; Sams, J.I.; Zupancic, J.W.; Schroeder, K.T. Tracking Solutes and Water from Subsurface Drip Irrigation Application of Coalbed Methane–Produced Waters, Powder River Basin, Wyoming. Environ. Geosci. 2011, 18, 169–187. [Google Scholar] [CrossRef]
  34. Hickey, L.J.; Yuretich, R.F. The Paleocene Chance Member of the Fort Union Formation, Northern Bighorn Basin, Montana and Wyoming: Aperiodic Cyclothems in a Tectonically Dominated Lake Basin. Mt. Geol. 2016, 53, 259–281. [Google Scholar] [CrossRef]
  35. Ellis, M.S. Quality of Economically Extractable Coal Beds in the Gillette Coal Field as Compared with Other Tertiary Coal Beds in the Powder River Basin, Wyoming and Montana; Open-File Report 2002-174; U.S. Geological Survey: Reston, VA, USA, 2002; p. 174. [CrossRef]
  36. McClurg, J.E. Peat Forming Wetlands and the Thick Powder River Basin Coals. In Annual Field Conference Guidebook, 39th ed.; Eastern Powder River Basin-Black Hills; Wyoming Geological Association: Casper, WY, USA, 1988; pp. 29–236. [Google Scholar]
  37. Moore, T.A. The Effects of Clastic Sedimentation on Organic Facies Development within a Tertiary Subbituminous Coal Bed, Powder River Basin, Montana, U.S.A. Int. J. Coal Geol. 1991, 18, 187–209. [Google Scholar] [CrossRef]
  38. Palmer, C.A.; Mroczkowski, S.J.; Kolker, A.; Finkelman, R.B.; Bullock Jr., J. H. Chemical Analysis and Modes of Occurrence of Selected Trace Elements in a Powder River Basin Coal and Its Corresponding Simulated Cleaned Coal; Open-File Report 2000-323; U.S. Geological Survey: Reston, VA, USA, 2001. [CrossRef]
  39. Milligan, C.; Reddy, K. Monitoring of Groundwater Contamination by Trace Elements from CBNG Disposal Ponds Across the Powder River Basin, Wyoming. J. Am. Soc. Min. Reclam. 2007, 520–527. [Google Scholar] [CrossRef]
  40. Wyoming State Engineer’s Office. Fort Union Formation Aquifer Monitoring Plan and Preliminary Aquifer Management Plan. Wyoming Water Development Commission: Gillette, WY, USA, 1995; p. 73. [Google Scholar]
  41. Burakov, A.E.; Galunin, E.V.; Burakova, I.V.; Kucherova, A.E.; Agarwal, S.; Tkachev, A.G.; Gupta, V.K. Adsorption of Heavy Metals on Conventional and Nanostructured Materials for Wastewater Treatment Purposes. Ecotoxicol. Environ. Saf. 2018, 148, 702–712. [Google Scholar] [CrossRef] [PubMed]
  42. Langman, J.B.; Sandlin, W.R.; Waynant, K.; Traver-Greene, M.; Moberly, J.G. Clinoptilolite and Iron Sorption/Desorption under Multiple pH Conditions: Testing a Substrate for Passive Treatment of Acidic, Iron-Rich Solutions. Water Environ. Res. 2021, 93, 1714–1721. [Google Scholar] [CrossRef]
  43. Pandová, I.; Panda, A.; Valíček, J.; Harničárová, M.; Kušnerová, M.; Palková, Z. Use of Sorption of Copper Cations by Clinoptilolite for Wastewater Treatment. Int. J. Environ. Res. Public Health 2018, 15, 1364. [Google Scholar] [CrossRef] [PubMed]
  44. Sandlin, W.R.; Langman, J.B.; Waynant, K.V.; Mukhopadhyay, M.; Thuneman, T.; Moberly, J.G. Comparison of APTES-Functionalized Silica Fiber and Clinoptilolite for Reducing Iron Concentrations in an Acidic Iron(II) Sulfate Solution: Potential Passive Treatment Substrates. Mine Water Environ. 2020, 39, 797–807. [Google Scholar] [CrossRef]
  45. Sandlin, W.; Langman, J.B.; Moberly, J.G. A Review of Acid Rock Drainage, Seasonal Flux of Discharge and Metal Concentrations, and Passive Treatment System Limitations. Int. J. Min. Reclam. Environ. 2020, 35, 34–47. [Google Scholar] [CrossRef]
  46. Holub, M.; Balintova, M.; Pavlikova, P.; Palascakova, L. Study of Sorption Properties of Zeolite in Acidic Conditions in Dependence on Particle Size. Ital. Assoc. Chem. Eng. 2013, 32, 559–564. [Google Scholar]
  47. Motsi, T.; Rowson, N.A.; Simmons, M.J.H. Adsorption of Heavy Metals from Acid Mine Drainage by Natural Zeolite. Int. J. Miner. Process. 2009, 92, 42–48. [Google Scholar] [CrossRef]
  48. Stylianou, M.A.; Hadjiconstantinou, M.P.; Inglezakis, V.J.; Moustakas, K.G.; Loizidou, M.D. Use of Natural Clinoptilolite for the Removal of Lead, Copper and Zinc in Fixed Bed Column. J. Hazard. Mater. 2007, 143, 575–581. [Google Scholar] [CrossRef]
  49. Wang, S.; Peng, Y. Natural Zeolites as Effective Adsorbents in Water and Wastewater Treatment. Chem. Eng. J. 2010, 156, 11–24. [Google Scholar] [CrossRef]
  50. Fischer, A.M.; Van Hamme, J.D.; Gardner, W.C.; Fraser, L.H. Impacts from Topsoil Stockpile Height on Soil Geochemical Properties in Two Mining Operations in British Columbia: Implications for Restoration Practices. Mining 2022, 2, 315–329. [Google Scholar] [CrossRef]
  51. Adams, M.B.; Archer, V.A.; Bailey, S.; McGuire, K.; Miniat, C.F.; Neary, D.G.; O’Geen, T.; Robichaud, P.R.; Strobel, M. Soils and Water. In Forest and Rangeland Soils of the United States Under Changing Conditions: A Comprehensive Science Synthesis; Pouyat, R.V., Page-Dumroese, D.S., Patel-Weynand, T., Geiser, L.H., Eds.; Springer International Publishing: Cham, Switzerland, 2020; pp. 33–49. ISBN 978-3-030-45216-2. [Google Scholar]
  52. Yi, Q.; Wu, S.; Southam, G.; Robertson, L.; You, F.; Liu, Y.; Wang, S.; Saha, N.; Webb, R.; Wykes, J.; et al. Acidophilic Iron- and Sulfur-Oxidizing Bacteria, Acidithiobacillus Ferrooxidans, Drives Alkaline pH Neutralization and Mineral Weathering in Fe Ore Tailings. Environ. Sci. Technol. 2021, 55, 8020–8034. [Google Scholar] [CrossRef]
  53. Doulati Ardejani, F.; Singh, R.N.; Baafi, E.; Porter, I. A Finite Element Model to Simulate Groundwater Rebound Problems in Backfilled Open Cut Mines. Mine Water Environ. 2003, 22, 39–44. [Google Scholar] [CrossRef]
  54. Dunrud, C.R.; Osterwald, F.W. Coal Mine Subsidence Near Sheridan, Wyoming. Environ. Eng. Geosci. 1978, 15, 175–190. [Google Scholar] [CrossRef]
  55. Karfakis, M.G.; Topuz, E. Post Mining Subsidence Abatements in Wyoming Abandoned Coal Mines. Min. Sci. Technol. 1991, 12, 215–231. [Google Scholar] [CrossRef]
  56. Naderian, A.R.; Williams, D.J.; Clark, I.H. Numerical Modelling of Settlements in Back-Filled Open-Cut Coal Mines. Int. J. Surf. Min. Reclam. Environ. 1996, 10, 25–29. [Google Scholar] [CrossRef]
  57. Sun, Q.; Zhou, N.; Quan, K.; Chen, Y. Stability Analysis and Control of Embankment with Solid Backfill Coal Mining. Min. Technol. 2017, 126, 104–112. [Google Scholar] [CrossRef]
  58. Zhang, J.; Li, M.; Taheri, A.; Zhang, W.; Wu, Z.; Song, W. Properties and Application of Backfill Materials in Coal Mines in China. Minerals 2019, 9, 53. [Google Scholar] [CrossRef]
  59. Technology Screening Matrix|Federal Remediation Technologies Roundtable (FRTR). Available online: https://www.frtr.gov/matrix/Solidification-and-Stabilization/ (accessed on 30 December 2024).
  60. U.S. Environmental Protection Agency. Method 1669, Sampling Ambient Water for Trace Metals at EPA Water Quality Criteria Levels; USEPA Office of Water Engineering and Analysis Division: Washington, DC, USA, 1996; p. 35.
  61. U.S. Geological Survey. National Field Manual for Collection of Water-Quality Data—Chapter A4. Collection of Water Samples; U.S. Geological Survey: Reston, VA, USA, 2006; p. 231.
  62. Lapakko, K.A. Developments in Humidity-Cell Tests and Their Application. In Environmental Aspects of Mine Wastes: Mineralogical Association of Canada Short Course Series; Jambor, J.L., Blowes, D.W., Ritchie, A.I.M., Eds.; Economic Geology Publishing Company: Littleton, CO, USA, 2003; pp. 147–164. [Google Scholar]
  63. ASTM C702/C702M-18; Standard Practice for Reducing Samples of Aggregate to Testing Size. ASTM International: Montgomery, PA, USA, 2018.
  64. ASTM D5744-18; Test Method for Laboratory Weathering of Solid Materials Using a Humidity Cell. ASTM International: Montgomery, PA, USA, 2018.
  65. Lapakko, K.A.; White, W.W. Modification of the ASTM 5744-96 Kinetic Test. In Proceedings of the Fifth International Conference on Acid Rock Drainage, Denver, CO, USA, 21–24 May 2000; Society for Mining, Metallurgy, and Exploration: Littleton, CO, USA, 2000; pp. 631–639. [Google Scholar]
  66. ASTM E105-16; Practice for Probability Sampling of Materials. ASTM International: Montgomery, PA, USA, 2016.
  67. ASTM D4644-16; Test Method for Slake Durability of Shales and Similar Weak Rocks. ASTM International: Montgomery, PA, USA, 2010.
  68. Baerlocher, C.; McCusker, L.B.; Olson, D.H. Atlas of Zeolite Framework Types, 6th ed.; Elsevier: Amsterdam, The Netherlands, 2007; ISBN 978-0-444-53064-6. [Google Scholar]
  69. Hunter, R.J. The Calculation of Zeta Potential. In Zeta Potential in Colloid Science; Academic Press: Cambridge, MA, USA, 1981; pp. 59–124. ISBN 978-0-12-361961-7. [Google Scholar]
  70. Roehler, H.W. Revised Stratigraphic Nomenclature for the Wasatch and Green River Formations of Eocene Age, Wyoming, Utah, and Colorado; Professional Paper 1506-B; U.S. Geological Survey: Reston, VA, USA, 1991. [CrossRef]
  71. Martin, P.L. Geological Investigations of the Vermillion Creek Coal Bed in the Eocene Niland Tongue of the Wasatch Formation, Sweetwater County, Wyoming; U.S. Geological Survey Professional Paper 1314-A-L; U.S. Geological Survey: Reston, VA, USA, 1987. [CrossRef]
  72. Ayers, W.B. Lacustrine and Fluvial-Deltaic Depositional Systems, Fort Union Formation (Paleocene), Powder River Basin, Wyoming and Montana. AAPG Bull. 1986, 70, 1651–1673. [Google Scholar]
  73. Hagmaier, J. Groundwater Flow, Hydrochemistry, and Uranium Deposition in the Powder River Basin, Wyoming. Ph.D. Thesis, University of North Dakota, Grand Forks, ND, USA, 1971. [Google Scholar]
  74. Szekeres, M.; Tombácz, E. Surface Charge Characterization of Metal Oxides by Potentiometric Acid–Base Titration, Revisited Theory and Experiment. Colloids Surf. Physicochem. Eng. Asp. 2012, 414, 302–313. [Google Scholar] [CrossRef]
  75. Drever, J.I.; Murphy, J.W.; Surdam, R.C. The Distribution of As, Be, Cd, Cu, Hg, Mo, Pb, and U Associated with the Wyodak Coal Seam, Powder River Basin, Wyoming. Rocky Mt. Geol. 1977, 15, 93–101. [Google Scholar]
  76. Jamieson, H.E. Geochemistry and Mineralogy of Solid Mine Waste: Essential Knowledge for Predicting Environmental Impact. Elements 2011, 7, 381–386. [Google Scholar] [CrossRef]
  77. Villeneuve, S.A.; Barbour, S.L.; Hendry, M.J.; Carey, S.K. Estimates of Water and Solute Release from a Coal Waste Rock Dump in the Elk Valley, British Columbia, Canada. Sci. Total Environ. 2017, 601–602, 543–555. [Google Scholar] [CrossRef]
  78. Bernhardt, E.S.; Lutz, B.D.; King, R.S.; Fay, J.P.; Carter, C.E.; Helton, A.M.; Campagna, D.; Amos, J. How Many Mountains Can We Mine? Assessing the Regional Degradation of Central Appalachian Rivers by Surface Coal Mining. Environ. Sci. Technol. 2012, 46, 8115–8122. [Google Scholar] [CrossRef] [PubMed]
  79. Bian, Z.; Dong, J.; Lei, S.; Leng, H.; Mu, S.; Wang, H. The Impact of Disposal and Treatment of Coal Mining Wastes on Environment and Farmland. Environ. Geol. 2009, 58, 625–634. [Google Scholar] [CrossRef]
  80. Zhao, L.; Ren, T.; Wang, N. Groundwater Impact of Open Cut Coal Mine and an Assessment Methodology: A Case Study in NSW. Int. J. Min. Sci. Technol. 2017, 27, 861–866. [Google Scholar] [CrossRef]
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Figure 1. Location of the Cordero Rojo Mine in the Powder River Basin of Wyoming, USA.
Figure 1. Location of the Cordero Rojo Mine in the Powder River Basin of Wyoming, USA.
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Figure 2. An example of the removal of overburden and waste generation during open-pit coal mining at the Cordero Rojo Mine, Powder River Basin, Wyoming, USA.
Figure 2. An example of the removal of overburden and waste generation during open-pit coal mining at the Cordero Rojo Mine, Powder River Basin, Wyoming, USA.
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Figure 3. Overburden formations and coal seam at the Cordero Rojo Mine, Powder River Basin, Wyoming, USA. The pit perspective and stepped wall distort the coal seam thickness (about 8 m) in relation to the overburden thickness (about 75 m).
Figure 3. Overburden formations and coal seam at the Cordero Rojo Mine, Powder River Basin, Wyoming, USA. The pit perspective and stepped wall distort the coal seam thickness (about 8 m) in relation to the overburden thickness (about 75 m).
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Figure 4. Sieving of Cordero Rojo Mine waste rock to ≤6.3 mm onsite.
Figure 4. Sieving of Cordero Rojo Mine waste rock to ≤6.3 mm onsite.
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Figure 5. Kinetic columns for benchtop experiments conducted with Cordero Rojo Mine waste rock.
Figure 5. Kinetic columns for benchtop experiments conducted with Cordero Rojo Mine waste rock.
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Figure 6. Major and trace element composition of the Fort Union and Wasatch waste rock from the Cordero Rojo Mine. * Total Fe expressed as FeO.
Figure 6. Major and trace element composition of the Fort Union and Wasatch waste rock from the Cordero Rojo Mine. * Total Fe expressed as FeO.
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Figure 7. Field parameter results for (a) Eh, (b) specific conductance, (c) pH, and (d) alkalinity of leachate from the (1) unamended column, (2) zeolite-amended column, (3) soil-amended column, (4) compaction column, and (5) rinsed column.
Figure 7. Field parameter results for (a) Eh, (b) specific conductance, (c) pH, and (d) alkalinity of leachate from the (1) unamended column, (2) zeolite-amended column, (3) soil-amended column, (4) compaction column, and (5) rinsed column.
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Figure 8. Anion concentrations for leachate from unamended, zeolite, soil, compacted, and rinsed waste rock columns for (a) chloride, (b) fluoride, (c) nitrate, and (d) sulfate.
Figure 8. Anion concentrations for leachate from unamended, zeolite, soil, compacted, and rinsed waste rock columns for (a) chloride, (b) fluoride, (c) nitrate, and (d) sulfate.
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Figure 9. Arsenic concentrations for leachate from (a) zeolite, (b) soil, (c) compacted, and (d) rinsed waste rock columns. Non-detection values were set to half the reporting limit (0.5 μg/L).
Figure 9. Arsenic concentrations for leachate from (a) zeolite, (b) soil, (c) compacted, and (d) rinsed waste rock columns. Non-detection values were set to half the reporting limit (0.5 μg/L).
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Figure 10. Cadmium concentrations in leachate from (a) zeolite, (b) soil, (c) compacted, and (d) rinsed waste rock columns for the first 18 days of the experiment. Non-detection values were set to half the reporting limit (0.5 μg/L).
Figure 10. Cadmium concentrations in leachate from (a) zeolite, (b) soil, (c) compacted, and (d) rinsed waste rock columns for the first 18 days of the experiment. Non-detection values were set to half the reporting limit (0.5 μg/L).
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Figure 11. Iron concentrations for (a) zeolite, (b) soil, (c) compaction, and (d) rinsed amended columns. Non-detection values were set to half the reporting limit (5 μg/L).
Figure 11. Iron concentrations for (a) zeolite, (b) soil, (c) compaction, and (d) rinsed amended columns. Non-detection values were set to half the reporting limit (5 μg/L).
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Figure 12. Mean particle size and ζ potential of leachate from the unamended, zeolite, soil, compacted, and rinsed waste rock columns for the first 55 days of the experiment.
Figure 12. Mean particle size and ζ potential of leachate from the unamended, zeolite, soil, compacted, and rinsed waste rock columns for the first 55 days of the experiment.
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Langman, J.B.; Martin, J. Kinetic Column Evaluation of Potential Construction Options for Lessening Solute Mobility in Backfill Aquifers in Restored Coal Mine Pits, Powder River Basin, USA. Hydrology 2025, 12, 8. https://doi.org/10.3390/hydrology12010008

AMA Style

Langman JB, Martin J. Kinetic Column Evaluation of Potential Construction Options for Lessening Solute Mobility in Backfill Aquifers in Restored Coal Mine Pits, Powder River Basin, USA. Hydrology. 2025; 12(1):8. https://doi.org/10.3390/hydrology12010008

Chicago/Turabian Style

Langman, Jeff B., and Julianna Martin. 2025. "Kinetic Column Evaluation of Potential Construction Options for Lessening Solute Mobility in Backfill Aquifers in Restored Coal Mine Pits, Powder River Basin, USA" Hydrology 12, no. 1: 8. https://doi.org/10.3390/hydrology12010008

APA Style

Langman, J. B., & Martin, J. (2025). Kinetic Column Evaluation of Potential Construction Options for Lessening Solute Mobility in Backfill Aquifers in Restored Coal Mine Pits, Powder River Basin, USA. Hydrology, 12(1), 8. https://doi.org/10.3390/hydrology12010008

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