MODIFICATION OF OXYGEN-CONSUMPTION TESTING FOR THE EVALUATION OF OXYGEN BARRIER PERFORMANCE

Version préliminaire – non publiée MODIFICATION OF OXYGEN-CONSUMPTION TESTING FOR THE EVALUATION OF OXYGEN BARRIER PERFORMANCE Bruno Bussière, Indust...
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MODIFICATION OF OXYGEN-CONSUMPTION TESTING FOR THE EVALUATION OF OXYGEN BARRIER PERFORMANCE Bruno Bussière, Industrial NSERC Polytechnique-UQAT Chair on Environment and Mine Waste Management, UQAT, Rouyn-Noranda, Québec Anne-Marie Dagenais, URSTM - Industrial NSERC Polytechnique-UQAT Chair on Environment and Mine Waste Management, UQAT, Rouyn-Noranda, Québec Mamert Mbonimpa, Industrial NSERC Polytechnique-UQAT Chair on Environment and Mine Waste Management, École Polytechnique, Montréal, Québec Michel Aubertin, Industrial NSERC Polytechnique-UQAT Chair on Environment and Mine Waste Management, École Polytechnique, Montréal, Québec

ABSTRACT: Covers with capillary barrier effects (CCBE) are now considered by the mining industry as a viable option for oxygen diffusion barriers. Different techniques have been proposed to evaluate the efficiency of an oxygen diffusion barrier used to control the production of acid mine drainage (AMD). One recent development is the Oxygen-Consumption (OC) method. The method consists of measuring the decrease in oxygen concentration over a relatively short period of time in an air filled chamber above the cover. This decrease in O2 concentration is then converted into an instantaneous oxygen flux by using fundamental Fick’s laws. However, this approach, developed initially to determine the oxidation rate of sulphide tailings, is not well adapted for a low oxygen flux like that observed through a CCBE. The standard OC method was modified by the authors to increase the precision of gas flux measurements through a cover. The study showed that the measurements with the modified approach give more realistic oxygen flux through a CCBE cover, when compared to the standard method. RÉSUMÉ : L’industrie minière considère maintenant les couvertures avec effets de barrière capillaire (CEBC) comme une méthode efficace pour limiter la diffusion de l’oxygène. Différentes techniques existent pour évaluer leur efficacité lorsque celles-ci sont construites pour limiter la formation de drainage minier acide (DMA). Parmi ces techniques, on retrouve une nouvelle méthode basée sur des essais consommation d’oxygène (OC). La méthode consiste à mesurer la diminution de la concentration en oxygène, pour une période de quelques heures, dans une chambre vide située audessus de la CEBC. Cette diminution de la concentration en O2 peut être convertie grâce aux lois fondamentales de Fick en flux d’oxygène quasi-instantané. Malgré ses avantages, la méthode OC, développée initialement pour déterminer le taux de réaction de résidus miniers sulfureux, n’est pas bien adaptée pour des faibles flux tels que ceux observés à travers les CEBC. Les auteurs ont donc modifié la méthode OC afin d’améliorer la précision des mesures à travers les recouvrements. Les modifications ont permis d’obtenir des valeurs de flux d’oxygène à travers la CEBC beaucoup plus réalistes que celles obtenues avec la méthode standard. 1.

INTRODUCTION

Covers with capillary barrier effects (CCBE) are now considered to be a viable option to limit gas migration. In the mining industry, such covers are used to limit the availability of oxygen to sulphide mine wastes. By limiting the oxygen flux through the cover, one can also limit the oxidation of sulphide minerals and consequently the production of acid mine drainage (AMD). To be efficient, the cover must maintain a high degree of saturation in one (or more) of its layers. The diffusion of gas through a nearly saturated soil is low enough to limit the production of AMD (e.g. Nicholson et al. 1989; Rasmuson and Erikson 1986; Aachib et al. 1994). Covers with capillary barrier effects (CCBE) usually contain three to five layers made of different materials. Each layer has to play one (or more) specific role(s). Figure 1 is a schematic illustration of a CCBE. The bottom layer is made of a fairly coarse material, which acts as both a mechanical support and a capillary break. The fine grained material, used as the moisture retaining layer, is

placed upon the first layer to create a capillary barrier effect. This effect is necessary to maintain a high degree of saturation in the moisture-retaining layer and to limit the ingress of oxygen. More details on capillary barrier effects can be found elsewhere (e.g. Rasmuson and Erikson 1986; Nicholson et al. 1989; Aubertin et al. 1995; Bussière 1999). Another coarse material is placed upon the finegrained material layer. The capillary barrier effects between the two materials prevent water loss by evaporation and help lateral drainage. The other two layers (protection and surface layers) are protective layers against erosion and bio-intrusion for the CCBE and are not further discussed in this paper. Because of the costs involved in the construction of a CCBE, it is necessary to monitor its effectiveness. Different techniques can be used to evaluate the efficiency of an oxygen diffusion barrier used to control AMD production. Measurement of the water quality in the covered waste and at the final effluent is one way to estimate the performance of the cover system. The water sulphate content can be converted in an equivalent pyrite oxidation rate by assuming that all sulphates are coming

Version préliminaire – non publiée from pyrite oxidation and that there is no significant sulphate accumulation in the waste. These two assumptions are not always valid due to the presence of other sulphide minerals in the mining waste (pyrrhotite, arsenopyrite, etc.) and to the precipitation of secondary minerals containing sulphates. Another disadvantage of this approach is the time (and space) lag between the measurements and the actual diffusion through the cover. Another way to estimate a cover performance consists of measuring the water content profile and evaluating the Fickian gas flux using the theoretical relationships between water content and the gas diffusion coefficient of unsaturated soils. The precision of this indirect approach is mainly dependent on the quality and representativity of the water content measurements. A new technique, called the Oxygen-Consumption (OC) method, has also been recently developed to evaluate the performance of an oxygen barrier. The main advantage of this direct technique is the almost instantaneous estimation of the oxygen flux. This paper briefly presents the standard OC method and discusses the problems of that technique for the determination of low gas fluxes similar to those observed through a CCBE. The proposed modifications to the testing procedure are then presented. The new interpretation method for the results of modified OC test is introduced, along with the details presented in a companion paper (by Mbonimpa et al., 2002 a; this Conference). Finally, in situ test results obtained with the standard and the modified OC method on an existing site covered by a CCBE made of non reactive materials are compared and analysed.

Surface layer

Protection layer Drainage layer

Moisture retaining layer Support layer

Elberling et al. (1994) and Elberling and Nicholson (1996) have proposed a new approach called the OxygenConsumption (OC) method to evaluate the oxidation rate of sulphide mine wastes. Basically, the concept of the OC test consists in measuring the decrease in oxygen concentration in a sealed air chamber placed over the reactive materials for a short period of time (usually between 2 and 5 hours). The decrease in oxygen concentration is due to the oxidation of pyrite and the corresponding rate can be calculated by using the oxygen depletion rate and the stoichiometry of the pyrite oxidation reaction. These measurements provide an almost instantaneous indication of the rate of oxidation under field conditions, regardless of climatic or moisture conditions in the tailings. Examples of field measurements with this technique can be found in the literature (e.g. Elberling et al., 1994; Nicholson et al., 1995; Elberling and Nicholson, 1996; Tibble and Nicholson, 1997). Later, Tibble and Nicholson, 1997 (see also Tibble, 1997) have proposed adapting the technique to measure the performance of an oxygen barrier. The consumption of oxygen in the chamber can be related to a cover’s ability to limit gas migration. Again, the technique provides an almost instantaneous determination of oxygen flux. However, there is difficulty with the OC tests performed on covers because it measures low oxygen fluxes (sometimes less than 2 mol O2/m²/year or 5.5x10-3 mol O2/m²/day) compared to the ones measured on reactive (sulphide) mine sites. Such low fluxes are often within the sensor range of precision. 2.1

Theory

The relation between oxygen flux through the cover and the decrease in oxygen concentration in the sealed chamber is based on fundamental gas diffusion laws (here, only Fickian gas transport mechanisms are considered). Details of the interpretation method for the standard OC method are given in Elberling et al. (1994) and Elberling and Nicholson (1996), and also in a companion paper (Mbonimpa et al., 2002a; this conference). Solving Fick’s second law expressed with a first-order kinetic reaction term for steady state flux and specified boundary conditions gives the following equation for the flux at the cover surface (Elberling et al., 1994) :

FL = C0 (K r De )

0.5

Tailings

Figure 1. Typical configuration of CCBE used in mining industry to limit oxygen diffusion (from Aubertin et al., 1995)

2.

STANDARD OXYGEN-CONSUMPTION TESTS

[1]

where Kr is the first-order reaction rate coefficient for the system (tailings with cover), De is the effective diffusion coefficient and C0 is the atmospheric concentration of oxygen. Solving the continuity equation (which reflects the oxygen being consumed in the head space) for the initial condition C = C0 at t = 0, the following solution is obtained:

C 0.5 A ln  = −t (K r De ) C V  0

[2]

Version préliminaire – non publiée where A and V are the area and the volume of the source reservoir respectively. The slope of the plot of ln (C/C0) versus time gives the value of (KrDe)0.5 when A/V is known. This term is substituted into equation 1 to evaluate the flux of oxygen at the surface. The standard OC test requires only a small change in oxygen concentration (2 to 3% O2) in the headspace over a one to three hour period so that changes in oxygen concentration within the pore spaces are insignificant during the testing period to comply with the interpretation assumption of steady state flux.

test is too small to give significant results, considering the precision of the sensor used. For this reason, the OC method was modified by the authors to evaluate low fluxes like those observed through a CCBE. Air filled chamber

Oxygen sensor

Isolated box Aluminium cylinder

Hh

2.2

In situ testing procedure

The in situ OC tests are performed here into 50 to 70 cm aluminium cylinders having a diameter of 14 cm. The cylinder is pushed into the cover until the bottom is embedded into the moisture-retaining layer, as shown in Figure 2a. It is assumed that there is no lateral gas movement (1D situation). To perform the test, a cap with an oxygen sensor is placed over the cylinder and the measurements are taken every 300 seconds for a period of 3 to 5 hours. The cap is shaded from the sun during the test by a box to reduce the fluctuation of the sensor. The type of oxygen sensor used in this study is the GC33-200 manufactured by GC Industries. The sensor is a galvanic electrochemical cell using the Pb-PbOOH half-cell to reduce oxygen (the consumption of oxygen by the sensor is negligible, see Tibble and Nicholson, 1997). The voltage produced by this reaction is directly proportional to the partial pressure of oxygen in the gas phase. The accuracy of the sensor is 0.1% O2 concentration. The selected volume of the air chamber, determined from eight measurements at eight different locations around the circumference of the cylinder, depends on the speed at which the oxygen concentration drops. The volume is smaller for low oxygen flux. Preliminary tests and calculations are necessary to determine an adequate volume. Usually, the best results come from having a reduction of about 3% in oxygen concentration during the test (Tibble and Nicholson, 1997). It is also important to account for the air in the void of the top layer for the evaluation of V. Neglecting this aspect can lead to an under-estimation of the flux. To do so, water content and in situ density measurements have to be made in the top layer and converted into an air void volume that must be added to the volume V of the air chamber.

3.

MODIFIED OXYGEN-CONSUMPTION METHOD

In spite of the advantages of the standard OC tests, this method was initially designed for determining reaction rates of sulphide tailings and is not well adapted for low oxygen fluxes as observed through a CCBE. For example, the decrease in oxygen concentration corresponding to a flux of 1.6 mol O2/m²/year (in a 14 cm diameter cylinder with a chamber height of 1 cm), which is typical of flux through an efficient CCBE (e.g. Aachib et al., 1994), is 0.1 % (the accuracy of the sensor) over a period of 3 hours. Hence, the variation in oxygen concentration during the

Drainage / protection / surface layer

Moisture-retaining layer

Support / capillary break layer

Acid generating tailings

a)

Air filled chamber

Oxygen sensor Isolated box

Control oxygen sensor

Aluminium cylinder

Drainage / protection / surface layer Hh

Moisture-retaining layer

Support / Capillary break layer

Acid generating tailings

b) Figure 2. Schematic representation of a) the standard OC test and b) the modified OC test 3.1

Modification to the in situ set up

The first modification consists of excavating the top layer of the CCBE to eliminate the uncertainties due to the air contained in the voids of the upper soil layer. The second modification is to use a longer cylinder to reach the reactive material at the bottom. This eliminates the possible effect of lateral movement of gas in the bottom desaturated coarse layer. The duration of the test is also changed; the modified OC test is performed over a period of four to five days. Furthermore, an oxygen sensor is placed in the isolated box and simultaneous

Version préliminaire – non publiée measurements are taken with the two sensors (the one in the air chamber and the one exposed to the atmosphere in the box) during the test. A correction is applied on the measurements to take into account the fluctuation of the sensor during the test by the aid of a control sensor (see Figure 2b). This fluctuation can be caused by different factors like ambient temperature, atmospheric pressure variations and the consumption of the GSI sensors during the four to five days test. Figure 2b presents a schematisation of the main modifications applied to the in situ set up.

where Hh is the height of the air chamber, Fs(t) is the flux through the surface and t is time. To calculate the evolution of the concentration in the air chamber, the software also needs some properties of the soils such as the equivalent porosity θeq and the bulk diffusion * coefficient D . The equivalent porosity θeq is employed here to take into account the flux in the air phase and the flux of oxygen dissolved in the water phase. It is defined as (Aubertin et al. 1999, 2000):

3.2

where H is the dimensionless Henry’s equilibrium constant (H ≅ 0.03 at 20°C), θa is volumetric air content in the soil * and θw is the volumetric water content. D can be expressed as a function of De and θeq:

Interpretation of the modified OC test

Because of the duration of the modified OC test, the hypothesis of steady-state conditions used in the standard OC test is no longer valid. To estimate the flux through the cover with the modified OC method, the use of numerical modelling is necessary. The software used in this study is POLLUTE (Rowe et al., 1998). This software solves the 1D governing equation for contaminant diffusion (here being O2) and with appropriate boundary conditions. In this case, the 1D boundary conditions are the source reservoir with an initial concentration in oxygen C0 (20.9 % or 8.71 mol O2/m³ of air) and the instantaneous consumption of oxygen by the sulphide tailings at the bottom. The variation in oxygen concentration in the source reservoir with time Ch(t) is expressed in the software by the following expression:

Ch (t ) = C0 −

1 Hh

t

∫ F (t )dt

[3]

s

0

θ eq = θ a + Hθ w

D* =

[4]

De

[5]

θ eq

By comparing the simulated and measured oxygen concentration in the air chamber, one can determine the parameters that give the best fit between the measured and the predicted results. For a non-reactive moistureretaining layer, the parameter used to fit the measured data is the diffusion coefficient D* and θeq. These fitted parameters can be subsequently used to calculate the flux of oxygen through the CCBE. The new approach also has the advantage of being able to deal with reactive moistureretaining layer. More details on the basic theory of the modified OC method and on the integration of the reactivity of the moisture-retaining layer are given in Mbonimpa et al. (2002a; this conference). The main differences between the standard and the modified OC method are summurized in Table 1.

Table 1. Main differences between the standard and the modified OC method for measurements through a cover Characteristics of the test Duration of the test Length of the cylinder Climatic effects Soil characteristics Interpretation Effect of oxygen consuming moistureretaining layer

4.

Standard OC method 1 to 3 hours 0.5 to 1m (must reach the moistureretaining layer of the cover) Non applicable Non applicable Steady-state assumption Non applicable

IN SITU RESULTS WITH THE TWO METHODS

In situ tests were performed in September 2000 on an existing CCBE constructed on the Lorraine site (Témiscamingue, Québec, Canada) to limit oxygen diffusion and therefore, the production of acid mine drainage. The main results are presented in the following sections. For in situ results on a CCBE made of low reactive materials, the reader is referred to the companion paper of Mbonimpa et al. (2002a; this conference).

4.1

Description of the test site

Modified OC method 4 to 5 days 1 to 1.5 m (must reach the sulphide tailings below the cover) Evaluated with a reference sensor Can be used to validate the results Interpretation by numerical modelling for transient conditions Can integrate a reaction rate for the moisture-retaining material

The Lorraine mine site, now a property of the Quebec Ministry of Natural Resources, was operated from 1964 to 1968 and generated approximately 600,000 tons of acid generating tailings that were disposed in a pond covering approximately 10 hectares. After an environmental study, it was decided to rehabilitate the site with a CCBE made of natural soils. The designed cover is composed of three layers: a base layer consisting of 30 cm of sand used as capillary break layer; a moisture-retaining layer made of silty material with a thickness of 50 cm; and a top layer consisting of a sand and gravel to protect the silt layer from evaporation and biointrusion (Nastev and Aubertin, 2000). Construction of the CCBE was done in late 1998 and 1999. Installation of instruments in the CCBE was

Version préliminaire – non publiée done in May 1999. The parameters monitored are volumetric water content and suction in the different layers of the cover. Figure 3 shows a plan view of the cover with all of the instrumented stations. In this study, 7 OC tests have been performed (test#2 to test#8) near existing stations (see Table 2). The locations of the test are identified in Figure 3 with an X. More details on the Lorraine site and the performance of the CCBE can be found elsewhere (e.g. Nastev and Aubertin, 2000; Dagenais et al., 2001; Aubertin et al., 2002; Dagenais, 2002).

POLLUTE are presented. The parameters used for modelling are presented in Table 3. Because volumetric water content in the moisture-retaining layer is usually different at the top than at the bottom (usually greater at the bottom), the moisture-retaining layer was divided into two layers called in Table 3 top silt and bottom silt. A finite oxygen concentration of 0.285 kg/m3 was specified with the height of the source reservoir (headspace of the air filled chamber) as the top boundary condition. The bottom boundary condition is specified as a constant concentration fixed at 0 kg/m3 (that is assuming all the oxygen is rapidly consumed by the reactive tailings underneath the cover). The thickness L of the moistureretaining layer integrated in POLLUTE for each modelling was the one measured in the field. The bottom sand layer was also included, but because of its low water content it doesn’t impede diffusion and so it has a minor role in the modelling. Figure 4 shows that it is possible to have a good representation of the measured results using numerical modelling. The oxygen concentration measured during the first three hours of the test were also recovered and analysed with the standard OC procedure. However, because of the small variations in oxygen concentration in the air chamber, the results were difficult to interpret. The linearity between ln (C/C0) and time was poor because of the low variation in oxygen concentration during the test (not shown here).

Figure 3. Plan view after reclamation of the Lorraine site showing the location of the instruments (from Dagenais et al., 2001) Table 2. Location of the seven tests performed Test# Location of the OC test 2

30 m East of B-6 Station

3

B-7 Station

4

North of PO 96-6 and West of PO 96-5 A-2 Station B-4 Station B-5 Station Between PO 96-5, B-5 Station and B-6 Station

5 6 7 8

4.2

Results

The main results obtained with the modified OC method for the seven tests performed on the Lorraine site are presented in Figure 4. These results (evolution of O2 concentration) are corrected for the fluctuation of the sensor exposed to the natural conditions. In this figure, the measured data and results predicted with the software

A comparison of the results obtained with the standard and the modified OC method is presented in Table 4. The flux of oxygen calculated with the modified OC method at the base of the moisture-retaining layer Fs,L was obtained with the following equation valid for steady-state conditions (Mbonimpa et al., 2002b):

Fs , L =

C0 De L

[6]

where De is the effective diffusion coefficient of the moisture-retaining layer evaluated with POLLUTE, L is the thickness of the moisture retaining-layer (it is assumed here that the sand layers have no significant effect on the migration of O2), and C0 is the concentration in air (0.285 kg/m3). In this calculation, a harmonic mean of the two De values is used for the entire silt layer. The results presented in Table 4 show that the flux of oxygen through the CCBE estimated with the two methods varies from 0.3 to 5.6 mol O2/m²/year for the modified OC method and from 8.4 to 70.4 mol O2/m²/year for the standard OC method. It is clear from these tests that the standard OC method tends to overestimate the oxygen flux through the cover (by a factor of 10 or more). The modified OC method gives more realistic results similar to the one predicted from the water distribution in the CCBE (e.g. Mbonimpa et al., 2002b). For a cover with a moisture-retaining layer of 0.5 m (like the Lorraine cover), the steady-state oxygen fluxes calculated for different degrees of saturation Sr typical of the ones measured at

Version préliminaire – non publiée the Lorraine site (85%, 90% and 95%; Dagenais et al., 2001, Aubertin et al., 2002) are 5.34, 1.42 and 0.154 mol/m²/year respectively. These values are in the range of

the ones measured with the modified OC method, which confirms the validity of the new approach proposed.

Test #3 O2 Concentration (kg/m 3)

O2 Concentration (kg/m 3)

Test #2 0.30 0.25 0.20 0.15 0.10 0

2000 4000 Elapsed tim e (m in) Measured POLLUTE

0.35 0.30 0.25 0.20 0.15 0.10 0

6000

0.30 0.25 0.20 0.15 0.10 0

2000 4000 Elapsed tim e (m in) Measured POLLUTE

0.30 0.25 0.20 0.15 0.10 0

6000

Test #6

2000 4000 Elapsed tim e (m in) Measured POLLUTE

6000

Test #7

0.30

0.30 3

O2 Concentration (kg/m )

O2 Concentration (kg/m 3)

6000

Test #5

0.35

O2 Concentration (kg/m 3)

O2 Concentration (kg/m 3)

Test #4

2000 4000 Elapsed tim e (m in) Measured POLLUTE

0.25 0.20 0.15 0.10 0

2000 4000 Elapsed tim e (m in) Measured POLLUTE

6000

0.25 0.20 0.15 0.10 0

2000 4000 Elapsed tim e (m in) Measured POLLUTE

6000

O2 Concentration (kg/m 3)

Test #8 0.30 0.25 0.20 0.15 0.10 0

2000 4000 Elapsed tim e (m in) Measured POLLUTE

6000

Figure 4. Measured and adjusted (with POLLUTE) oxygen concentration decrease in the air chamber for the tests performed on the Lorraine CCBE

Version préliminaire – non publiée Table 3. Parameters used in the numerical modelling

0,072

2 D* (m /s) (top silt) 2,56E-07

D* (m2/s) (bottom silt) 2,86E-07

0,025

3,76E-08

3,66E-08

0,041 0,023 0,024 0,016 0,074

7,15E-08 1,01E-07 1,24E-07 5,41E-08 1,31E-07

7,89E-08 6,76E-08 1,01E-07 2,70E-08 1,56E-07

Test #

L (m)

Hh (m)

θeq (top silt)

θeq (bottom silt)

2

0.74

0,0306

0,044

3

0.65

0,0356

0,027

4 5 6 7 8

0.74 0.71 0.71 0.71 0.71

0,0285 0,0333 0,0255 0,0207 0,0255

0,031 0,041 0,034 0,032 0,041

Table 4. Comparison between the oxygen flux obtained with the standard and the modified OC method Test#

Modified OC method

Standard OC method

Mol O2/m²/year (kg O2/m²/year) 2 3 4 5 6 7 8

5.

-1 5.6 (1.8x10 ) 0.4 (1.3x10-2) 1.0 (3.2x10-2) 0.9 (2.9x10-2) 1.2 (3.9x10-2) 0.3 (8.6x10-3) 2.9 (9.3x10-2)

CONCLUSIONS

The evaluation of the performance of an AMD control method is a key component for the rehabilitation of a mining site. Low fluxes are difficult to measure by the standard OC method because of limits inherent to the measurement technique and interpretation. In many cases, the differences in oxygen concentration over a short period of time (in a source reservoir over a CCBE) are within the measurement variation error of the sensor. The authors have presented a modified version of the Oxygen-Consumption method to measure low oxygen flux like the one observed through covers with capillary barrier effects used to limit AMD production. The main modifications to the testing procedure are related to the length of the cylinder, the removal of the top sand layer, and the duration of the testing period. The interpretation of the results is also different and is based on numerical modelling of gas diffusion. Integrating these modifications to the Oxygen-Consumption test allows for more precise measurement of the oxygen flux trough the cover and a better evaluation of the cover’s performance. The oxygen fluxes measured by this method are more realistic and better correspond approximately to the one calculated from the moisture distribution in the cover. Moreover, the modified OC method takes into account all the heterogeneities of the layer while the flux evaluated from water content in the layers of the cover is based on a limited number of volumetric water content and porosity measurements.

8.4 (2.7x10-1) 29.5 (9.4x10-1) 31.5 (1.0) 45.9 (1.5) 70.4 (2.3) 57.1 (1.8) 70.4 (2.3)

6.

AKNOWLEDGMENTS

Funding for this work came from a number of sources including the FCAR (individual grant, B. Bussière), the Quebec Ministry of Natural Resources, the industrial NSERC Polytechnique-UQAT Chair on Environment and Mine Waste Management, and the FUQAT (Fondation de l’Université du Québec en Abitibi-Témiscamingue).

7.

REFERENCES

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Version préliminaire – non publiée AUBERTIN, M., CHAPUIS, R.P., AACHIB, M., BUSSIÈRE, B., RICARD, J.-F., and TREMBLAY, L. (1995). Évaluation en laboratoire de barrières sèches construites à partir de résidus miniers, MEND Report 2.22.2a. BUSSIÈRE, B. (1999). Étude des écoulements nonsaturés à travers les couvertures avec effets de barrière capillaire. Ph.D Thesis, Department of Civil and Geological and Mining Engineering, École Polytechnique de Montréal, Québec. DAGENAIS, A.-M. (2002). Techniques de contrôle du drainage minier acide basées sur les effets capillaires. PhD. Thesis, Department of Civil and Geological and Mining Engineering, École Polytechnique de Montréal, Québec (In progress). DAGENAIS, A.-M., AUBERTIN, M., BUSSIÈRE, B, BERNIER, L. and CYR, J. (2001). Monitoring at the Lorraine Mine Site : a Follow Up on the Remediation Plan. Proceeding of the National Association of Abandonned Mine Land Annual Conference, CD-ROM. ELBERLING, B. and NICHOLSON, R. V. (1996). Field determination of sulfide oxidation rates in mine tailings. Water Resources Research, 32 : 17731784. ELBERLING, B., NICHOLSON, R.V., REARDON, E.J. and TIBBLE, P. (1994). Evaluation of sulphide oxidation rates: laboratory study comparing oxygen fluxes and rates of oxidation product release. Canadian Geotechnical Journal, 31: 375-383. MBONIMPA, M., AUBERTIN, M., AACHIB, M., and BUSSIÈRE, B. (2002). Oxygen Diffusion and Consumption in Unsaturated Cover Material. Canadian Geotechnical Journal (Submitted, December 2001). MBONIMPA, M. AUBERTIN, M., DAGENAIS, A-M. and BUSSIÈRE, B. (2002). Interpretation of field tests to determine oxygen diffusion and reaction rate coefficients of tailings and soil covers. (these proceedings) NASTEV, M., AUBERTIN, M. (2000). Hydrogeological modelling for the reclamation work at the Lorraine mine site Québec. Proceedings of the 1st Joint IAHCNC-CGS Groundwater Specialty Conference, Montréal, 311-318. NICHOLSON, R.V., ELBERLING, B. and WILLIAMS, G. (1995). A new oxygen consumption technique to provide rapid assessment of tailings reactivity in the field and the laboratory. Proceedings of the Sudubury’95 Conference, Sudbury, 999-1006. NICHOLSON, R. V., GILLHAM, R. W., CHERRY, J. A., and REARDON, E. J. (1989). Reduction of acid generation in mine tailings through the use of moisture-retaining cover layers as oxygen barriers. Canadian Geotechnical Journal, 26, 1-8. RASMUSON, A. and ERIKSON, J.C. (1986). Capillary barriers in covers for mine tailings dumps. Report 3307, The National Swedish Environmental Protection Board.

ROWE, R.K., BOOKER, J.R., FRASER, M.J. (1998). POLLUTEv6.3.5 and POLLUTE-GUI User’s Guide. GAEA Environmental Engineering Ltd., London, Ontario, 326 p. TIBBLE, P.A. (1997). A survey of in situ oxygen consumption rates for sulphide tailings : investigations on exposed tailings and selected remediation efforts. Thesis Master of Science in Earth Sciences, University of Waterloo. TIBBLE, P.A. and NICHOLSON, R.V. (1997). Oxygen consumption on sulphide tailings and covers : measured rates and applications. Proceedings of the Proceedings of the 4th International Conference on Acid Rock Drainage, Vancouver, Vol. 2, 647661.

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