assessing the impact of waste rocks on groundwater ...

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in horst zone, in the productive geological formation of Westphalian C. The mining activity has generated along. 65 years (1936-2001), 15 to 20 millions tons of ...
Bendra B et al. / International Journal of Engineering Science and Technology (IJEST)

ASSESSING THE IMPACT OF WASTE ROCKS ON GROUNDWATER QUALITY IN THE ABANDONED COAL MINE OF JERADA CITY (NORTH EASTERN MOROCCO) BENDRA B.1,2, SBAA M. 1, FETOUANI S. 1 and LOTFI A. 2 1: Université Mohamed Premier (UMP). Centre Oriental des Sciences et Technologies de l’Eau (COSTE), Boîte postale n° 524, code postal 60.000, Oujda, MAROC 2 : Université de Franche Comté (UFC), Laboratoire de Chrono-environnement USC INRA, UMR CNRS 6249. 1, Place Leclerc F-25030 Besançon cedex .FRANCE. E-mail: [email protected] Abstract The exponential growth of urban dwellers calls for an increased awareness of urban ecosystems and appropriate, long-term management practices. Especially the water supply needs to be secured, both in terms of quantity and quality. In Morocco, numerous urban mine sites were abandoned regardless rehabilitation strategy. Consequently, mining activity contributes massively to deteriorate air, soil and water quality, to degrade natural ecosystems and to menace public health. The abandoned coalmine of Jerada is located in north east of Morocco, in horst zone, in the productive geological formation of Westphalian C. The mining activity has generated along 65 years (1936-2001), 15 to 20 millions tons of washery waste rocks, cumulated principally in urban center. The groundwater (n=30) and waste rock (n=7) sampling was led in the middle of May 2008, which presents in local climatic context the end of rainy season and the beginning of sec season. Waste rocks are exhaustively black schist, with a paucity in pyrite (anthracite debris contain between 2 to 5% of synergic pyrite) and predominance of calcareous minerals essentially as dolomite. Consequently, the majority of waste rock samples are not acid generators. The pyrite oxidation produces sulphuric acid, which will be quickly neutralized by carbonates. The alkaline tendency of pH classifies Jerada abandoned coal mine in circum neutral mining drainage type (NMD). The leaching through unsaturated and saturated zone will be facilitated due to a big pore size and a breaking tectonic having fractured Jerada coal basin. The deformed black schist alternative to sandstone permits a good water circulation. The massive product of mining drainage and the major pollutant of groundwater is

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undoubtedly S-SO4 (27/30 exceed WHO guideline). The spatial correlation between S-total and salinity illustrates the deterioration of groundwater quality due to pyrite oxidation. The alteration of schist and halite dissolution contribute to enrich groundwater in chloride (26/30 exceed WHO guideline). The quasi-absence of sewage disposal contaminates groundwater in N-NO3 (18/30 exceed WHO threshold). Metallic pollution of groundwater is geographically very restrained (1/30 to 3/30 exceed slightly WHO guidelines), due to the precipitation of metallic elements under hydroxide form. The recourse of groundwater use as drinking water in 7/30 of cases constitutes a real menace for public health (purgative effect due to S-SO4 and methemoglobinemia due to N-NO3); making sensitive Jerada population proves to be an urgent necessity.

Key words: sulphate, nitrate, mining spoils, purgative effect, methemoglobinemia.

I. Introduction Urban dwellers currently account for 48.7% of the total population, compared to 29% of the total population in 1950 (UN Population Division, 2005). This background calls for an increased awareness of urban ecosystems and appropriate, long-term management practices. Especially the water supply needs to be secured, both in terms of quantity and quality (Wolf L., 2007). In Morocco, numerous urban mine sites were abandoned regardless rehabilitation strategy. Consequently, mining activity contributes massively to deteriorate air, soil and water quality, to degrade natural ecosystems and to menace public health (Moroccan ministry of energies and mines, 2002; Rheyati N., 2002). The Jerada coal mine was abandoned on 2001, operating since 1936 and considered after the closure of Kenadsa coal mine in Algeria (1962), the only one operating coal field in North Africa (Owodenko B., 1976). This coal mining district produced during 41 years (1960-2001) 509 146 tons of anthracite per annum and generated annually between 500.000 and 600.000 tons of overburden dumps and coal washery wastes, equivalent to a cumulative mass averaging 15 to 20 millions tons (Benkhadra A. and El Abbaoui A., 2006; Owodenko B., 1976; Moroccan ministry of agriculture, rural development, water and forests, 1996). The proceeding to mine closure was caused by difficult basin morphology and cheapness of coal importation price (Elouadi, 2002). An informal exploitation was carried after mine closure; with a weak production approximates 300 tons per annum destined for regional related industries. This underground deeper coal mine (>80m of depth) is an anthracite containing 2–5% of synergistic pyrite in fine to medium size grains (Vermeulen and Usher, 2006; Owedenko, 1976). Mining spoils are composed principally by dark schist, which affects considerably panoramic view of Jerada city (strip-mining). During rainy season a gaseous emission

ISSN : 0975-5462

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Bendra B et al. / International Journal of Engineering Science and Technology (IJEST)

(sulphur oxide) from mining spoils is usually observed (self-heating) and sometimes spontaneously small explosions detonates (Moroccan ministry of agriculture, rural development, water and forests, 1996). Sulphide minerals, mainly pyrite (FeS2), which are often present in mine wastes can generate Acid Mining Drainage (AMD) when they come in contact with water, oxygen and bacteria such as Thiobacillus ferroxidans. The oxidation of pyrite produces sulphuric acid (H2SO4) reducing pH in solution (1). Subsequently, the regional geological context, rich in calcareous crust deposit neutralised acid in the drainage (2) (Raynal, 1961; .Ruellan, 1971; Benzaazoua and all, 2002). (1) FeS2 + 15/4O2 + 7/2H2O → Fe(OH)3 + 2H2SO4 (2) 2CaCO3 + 2H2SO4 → 2CaSO4 + 2CO2 + 2H2O The present research paper aims (i) to assess globally groundwater quality and elucidate amongst pollution sources the impact of waste rocks (ii) to investigate groundwater uses and probable menace for public health via a questionnaire (iii) to suggest some practical moves in order to reduce pollution pressure (iv) to serve as a document for further studies focusing on environmental problematic in the present abandoned coal mine. II. Material and methods 1. Study area presentation Jerada coal mine is located in north east of Morocco, 60 km to the south of Oujda city (Fig.1). The coal deposit has been discovered at 1927. It extends on a 15 ha surface area and a thickness of 95 m. The climate of Jerada city is typically Mediterranean, semi-arid with cold rainy winter and warm sec summer (Lâaouina, 1990). The medium of rainfall averages 141.36 mm per annum (DHO, 2005). The Jerada Basin is located in the “horst zone” of eastern Morocco. During Early Visean times, a graben system opened up between two continental horsts in the Jerada area (Desteucq, 1982). The total thickness of the Westphalian C series is 500 m (Owedenko, 1976; Desteucq et al., 1988; Izart, 1990; Essamoud and Courel, 1996). Eight main coal seams (0.2 -l m thick) are identified and labelled A-H (Fig.2). Two marine levels (S and D), result of two marine incursions, containing goniatites, lamellibranchiata, brachiopoda and foraminifera are inter-bedded in the predominantly elastic continental series (Owedenko. 1976).

2. Sampling strategy and water analysis Seven sampling locations were selected in mine district, labelled respectively: WC, SHWR, BHWR, WR1, WR2, WR3 and RS. WC presents a soil with white crust frequently and generally observed into local soils. SHRW and BHWR present the summit and the basis of the highest waste rock dump (1114m). WR1, WR2 and

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WR3 are ordinary waste rock locations differently distributed in space. RS is a soil sampled in the old decantation dam, which was used by the local power plant to cold down machines. This site was rehabilitated by a fine sandy cover, vegetated by Nerium oleander and irrigated by drop to drop system (Fig.3). The mining spoils samples were collected at a depth of 0 to 30 cm from seven locations in the study area. In the first time the residual humidity was measured by loss water at 105°C (NF ISO 11465), after these samples were air dried and analyzed as follows: pH in a 1:5 weight spoil and distilled water using a pH-meter (WTW530, LUTRON salinity and conductivity in a 1:5 volume spoil and distilled water using (COND 330i, LUTRON

TM

TM

),

), The

granulometric analysis was done by sieves method (NF X 11-506/507). The results of a sieve analysis are plotted as cumulative weight versus sieves pore size (semi-logarithmic plot). This presentation permits by interpolation the determination of pore sizes d10, d30 and d60 for which 10%, 30% and 60% of the particles are finer. Calculating the coefficients of uniformity (Cu= d60 /d10) and curvature (Cc= (d30)2 / d60*d10) requires grain diameters. The intrinsic permeability was estimated by use of an empirical formula (Ki= CH.d102) cited in (Hazen, 1892; Hazen, 1911). The value of CH is usually assumed to be equal to 100 (David Carrier III W., 2003). Hazen formula is valid mainly for gravels and clean sands with a coefficient of uniformity (Cu) less than about 2 (Terzaghi and Peck 1964). Mining spoils bulk density of the disturbed samples was measured using a small cylinder of 100 cm3 (Baize, 2000). Calcareous was measured by the calcimeter of Bernard (CIRAD, 2004). Total nitrogen by macro-Kjeldahl digestion, mineral nitrogen in a 1:5 by weight of spoil and solution of potassium chloride, NH4-N (Afnor T90-015), NO3-N (Afnor T90-012), NO2-N (Afnor T90-013), sulphates (Afnor T90009), PO4-P (Afnor T90- 023); organic matter by loss on ignition (MA. 1010 – PAF 1.0). All metallic elements (Al, As, Ca, Cd, Cr, Cu, Fe, k, Mg, Mn, Na, Ni, Pb, S, Si, Zn, Hg) were measured by ICP method in UTARSCNRST laboratory in Rabat. The Maximum Potential Acidity (MPA) and Acide Neutralizing Acidity (ANA) were calculated using Acid-Base Account method (Sobek and all, 1978). The groundwater samples were collected in polyethylene bottles of 1litre. Before sampling, the recipient was cleaned several times using the well water. Recipients were gradually filled to avoid turbulences and aeration during the sampling. To avoid sampling artefacts and analytical artefacts, in particular the gain of dissolved gas and microbiological activity, water samples were immediately cooled at 4°C using portable icebox. Analysis was further performed as fast as possible and this within 24 h after sampling. The analytical method for NH4+-N dosage is the method of Solorzano and Koroleff (cited in Afnor T90-015) which is a very sensitive method for low NH4+-N content in the liquid phase. NO2-N was determined through the diazotation with sulphanilamide (Afnor T90-013), NO3-N with the method based on sodium salicylate (Afnor T90-012). For the determination of

ISSN : 0975-5462

Vol. 3 No. 11 November 2011

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Bendra B et al. / International Journal of Engineering Science and Technology (IJEST)

PO4-P, use was made of the colorimetric method (Afnor T90- 023). Other mineralogical properties have been determined following the French system of normalisation (Afnor): chloride (AfnorT90-014), sulphates (Afnor T90-009), the calcium and magnesium (Afnor T90-016), sodium (Afnor T90-019), and potassium (Afnor T90020). The electric conductivity and salinity are measured with a conductivity meter (COND 330i, LUTRON TM). The pH is measured directly in water by a pH-meter (WTW530, LUTRON

TM

). When samples were collected,

ground water position was measured and used to establish aquifer depth map (Fig.4). All sampling was performed in 16 March 2008. A questionnaire about groundwater uses was filled out concurrently to sampling. Acknowledgement: Miss.Ouaddari, from UATRS-CNRST, is acknowledged for his technical assistance. 3. Statistical modeling Principal component analysis (PCA) was used to analyse the correlation structure between the set of soil quality parameters collected during the survey. The PCA adopted in this paper was based on normalised and standardised data and exploits the correlation matrix between soil quality parameters rather than the covariance matrix. The PCA analysis was performed using the statistical toolbox available in MATLAB7TM. The spatial correlation was explored using semi-variogram analysis. The semi-variogram was modelled using Gaussian model. All the geostatistical analysis were performed using the BME statistical toolbox for MATLAB7TM (Christakos et al., 2002). The chemical speciation was explored using PHREEQC 2TM, which is a computer program for simulating chemical reactions and transport processes in natural or polluted water. The program is based on equilibrium chemistry of aqueous solutions interacting with minerals. It permits the calculus of molalities and saturation indices (SI), SI>0 specifies super-saturation and SI