INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 4, No 5, Copyright by the authors - Licensee IPA- Under Creative Commons license 3.

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1 INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 4, No 5, 2014 Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0 Research article ISSN Evaluating drastic method for assessing Spoil heap groundwater contamination vulnerability Geological engineer m.h.moustafa@gmail.com doi: /ijes ABSTRACT DRASTIC method used to assess groundwater contamination vulnerability based on different factors controlling contaminates transport at ground surface from agriculture and industrial activities to groundwater water table. This work evaluates DRASTIC method for assessing groundwater contamination vulnerability from acid water generation due to pyrite oxidation in spoil heap. The DRASTIC method assumptions and the factors used in this method were discussed to examine its suitability for assessing contamination vulnerability from acidic water in the spoil heap. Factors used in DRASTIC approach, depth to water, rainfall, aquifer media, surface topography, hydraulic gradient and hydraulic conductivities were collected from monitoring boreholes network in the spoil heap located in northern England. Not all drastic factors concepts applicable to spoil heap cases. DRASTIC method may be not suitable for assessing vulnerability to contamination due to acid water generation from spoil heap and it may give highly uncertain results if applied in spoil heap case. Keywords: vulnerability, acid mine drainage, DRASTIC, spoil heap. 1. Introduction Groundwater contamination is not only a serious environmental issue but also an economic and human health problem. Evaluating groundwater pollution and prevention before pollution occurs contribute to reducing contaminants in the source water. Contamination of water comes from different resources such as industrial and agricultural activities. Acid mine drainage, AMD, describes waters which have been affected in the pyrite oxidation processes in mined ground. Acidic mine drainage is a substantial environmental problem worldwide and is especially well documented in the UK. In the UK, abandoned coal and metal mines are the main sources of acidic mine drainage (Younger et al., 2002). When pyrite is exposed to oxygen and water from rainfall it will be oxidized, resulting in acidity in form of hydrogen ion, high sulfate and metals concentrations such as ferrous iron (equation 1) Fe S2 (s) + 7/2 O2 + H2O = 2SO Fe H + [1] From equation (1) every mole of oxidized pyrite will release two moles of proton acidity (i.e. H + ). The Fe (II) released by pyrite oxidation may be further oxidized to Fe (III) if there is enough O2 (reaction 2). Oxidation of Fe (II) to Fe (III) is slow at low ph. Fe /4O2 + H + = Fe 3+ + ½ H2O [2] (e.g Jambor, 1994; Nordstrom and Alpers, 1999; Singer and Stumm, 1970). Pyrite oxidation waters displaced downward into the saturated zone can be low in ph and contain high Received on February 2014 Published on April

2 concentration of Fe (II), SO4-2 and H +. Aquifer vulnerability is the intrinsic characteristics which determine the sensitivity of different parts of the aquifer to be affected by contamination (Foster & Hirata,1988). There are different approaches for groundwater contamination vulnerability assessment (a) simulation approaches using simulation models to simulate flow and contaminants transport (Magiera,2002 ; Thapinta & Hudak, 2003); (b) generating groundwater vulnerability maps based on observed contaminants; (c) statistical methods to correlate spatial variables with the actual occurrence of pollutants in groundwater (Babiker et al., 2005); and (d) index map or overlay method combining the factors controlling the contaminates transport in the saturated zone and resulting in spatially-distributed vulnerability indices. However, index or overlay method have drawback due to the subjectivity in assigning the factor weighting and assignment of numerical values. In the same time this method has advantages in the availability of its parameters used such as rainfall, hydraulic conductivity and depth to water (Thapinta and Hudak, 2003). The DRASTIC method, an index method, was developed by the US Environmental Protection Agency (EPA) (Aller et al., 1987). DRASTIC includes seven factors: Depth to water, (D) Net recharge( R), Aquifer( A), Soil media( S), Topography (T), Impact of vadose zone( I), Hydraulic conductivity of the aquifer ( C). These factors are describing the hydrogeologic setting in the site under study. DRASTIC method provides a numerical ranking composite description of the seven factors controlling groundwater movement into the unsaturated zone of an area to groundwater table. According to the importance of each factor in groundwater contamination process, it was assigned a weight ranging from 1 to 5. These score of weight quantifies the opinions of single or multiple experts in the role or importance of the factor in the contamination process. The most significant factor has a weight of 5 and the least significant one has a weight of 1. Normally Geographic information system used to produce overall vulnerability index map representing the vulnerability to contamination in the study site. DRASTIC method is the widely used for groundwater vulnerability (e.g Worrall & Kolpin, 2004; Babiker et al., 2005, Worrall, F. & Besien T., 2005). GLA method was developed by Geological survey of Germany (Hoelting et al., 1995), this method was develop for Karts infiltration to PI method (Goldscheidr, 2002). The present work assesses the effectiveness of DRASTIC method in assessing` the vulnerability of spoil heap groundwater to contamination from acidic water developed in the spoil heaps once rainfall penetrates it. 1.1 Site location Shilbottle old Colliery lies north Newcastle, UK (Figure 1). The associated spoil heap attained a maximum height of 27 meters above ground level and was disposed in two areas; an eastern heap along the banks of the Tyelaw Burn, a tributary of the River Coquet, and a smaller heap to the west (Fig. 2). The colliery spoil heap consists of both coarse and fine wastes discarded during mining operations mainly Pyrite mineral. When rainfall percolates into spoil, pyrite inside the spoil oxidized in the unsaturated zone and acidic water generated with low Ph and high metals concentrations such as Fe and high SO4 concentrations. This acidic water transports to saturated zone (main groundwater system) in the spoil, polluting the groundwater system in the spoil which drains to the Tyelaw Burn. 1040

3 Figure 1: Spoil heap location Figure 2: Spoil heap Sketch layout 2. Material and methods DRASTIC factors; depth to water, hydraulic conductivity, topography survey were carried out and collected from monitoring boreholes network in the spoil heap Fig (3). Aquifer material investigated from borehole drilling cuttings. The depth to water was measured using water dipper, Geochemistry parameter and metal concentrations were monitored. A pumping test using wattera pump were carried out in 5 cm diameter monitoring boreholes to obtain hydraulic conductivity of the spoil, the pumping data were analyzed using (Theis recovery,1935). 1041

4 Figure 3: Monitoring boreholes network 3. Result and conclusion Drastic approach assumes contaminants applied to ground surface, in case of spoil heaps the contaminants developed once rainfall penetrates the spoil and oxides pyrites. So if the contaminants applied just beneath ground surface as in case of spoil heap it is believed not violate DRASTIC assumption. From drilling cuttings investigation, Spoil heap consists of mainly from pyrite with intercalation of clay. Drastic factors concepts and its applicability to groundwater vulnerability in spoil heap were discussed: 3.1 Depth to water In DRASRTIC approach concepts, a deeper depth to water table means low probability for groundwater contamination due to the greater opportunity for natural attenuation (Aller et al., 1987). However, in spoil heap in the study site the longer depth to water the more possibility for pyrite oxidation and the more probability of generation acidic water and high level of contaminates. This is noticed in spoil heap at study site where some boreholes with deeper depth to water have high metals concentrations (Table 1). This is may be due to lack of buffering materials inside the spoil heap. 1042

5 Table 1: Depth to water and contaminates in groundwater Borehole name Total Fe mg/l Depth to water (m) U U U U Net recharge In DRASTIC approach concepts, higher recharge means higher probability of groundwater contamination. This may agree with the acid generation in spoil heap, where the higher rainfall recharge the higher pyrite oxidation and more generation of acidity consequently high metals concentration and high contamination potential. However, drastic approach did not take into account the net alkalinity/acidity of recharge water. If the spoil receive net alkaline recharge from adjacent aquifer or any source, it will promote the natural attenuation process and reduce contaminates concentrations reach to groundwater consequently no high pollution vulnerability. The spoil heap receive neutral recharge water from adjacent aquifer ( Moustafa et al,2005). This was noticed in some boreholes have high Ph and low Iron concentrations (Table 2). Table 2: PH and Fe concentration values measured in monitoring boreholes Borehole name Total Fe Ph value U4 12** 6.52 U5 23** 6 U7 115* 5.57 U8 48* 6.51 * Boreholes very near from neutral recharge water (farm land border) ** Boreholes receive high recharge neutral water due to high permeability. 3.3 Hydraulic conductivity DRASTIC approach concepts, states that, the higher aquifer permeability the higher groundwater contamination potential. This is may not agree with spoil heap case. Where from monitoring water chemistry and the measured hydraulic conductivity in spoil boreholes, it was noticed that some boreholes with high permeability have high Ph value and low metals concentrations such as U4 and U5 boreholes (Table 3). This may be due to high hydraulic conductivity of spoil lead to receive high neutral recharge water from adjacent aquifer, which works as buffering agent to the developed acidic water in the unsaturated zone of the spoil. 1043

6 Table 3: Hydraulic conductivities boreholes and ph values 3.4 Impact of vadose zone media Borehole name Hydraulic conductivities m/d ph value U U In Drastic approach concept, the less thickness of vadose zone and high permeability the higher probability for contamination. This is may not adaptable in spoil heap cases, where short thickness of unsaturated zone and high permeability means no enough residence time in the vadose zone for pyrite oxidation and developing acidic water consequently no or less probability to groundwater contamination in the spoil heap. Long length of vadose zone and low permeability is believed the main reason for pyrite oxidation and generation of acidic water consequently more chance for groundwater contamination. 4. Topography In drastic approach concepts, flat slopes provide a greater opportunity for contaminates percolation into main groundwater body and hence high probability for contamination. This is adaptable to spoil case. Where flat slopes implies high chance for rainwater infiltration and generating acidic water once contact with pyrite inside the spoil polluting groundwater in the heap. 5. Conclusions Not All DRASTIC approach factors can be applied to assess spoil heap groundwater vulnerability to contamination from acidic water developed inside spoil heaps especially with no buffering material in the vadose zone. If this method applied in spoil heap cases it may give highly uncertain results. Drastic did not consider net alkalinity/acidity nature of net recharge. 6. References 1. Aller, L., Bennett, T., Lehr, J.H., Petty, R.J. & Hackett, G. (1987), DRASTIC: A standardized system for evaluating groundwater pollution potential using hydrogeologic settings. EPA/600/2-87/035, US Environment Protection Agency, Ada, Oklahoma, USA. 2. Babiker, I. S., Mohamed, M. A. A., Hiyama, T. & Kato, K., (2005), A GIS-based DRASTIC model for assessing aquifer vulnerability in Kakamigahara Heights, Gifu Prefecture, central Japan. Sci. Total Environ. 345, pp Foster.S.& Hirata,R.,(1988),Groundwater pollution Risk Assessment-A Methodology uing Avialable data Pan American Centre for Salinity Engineering Sciences, p.73. Lima/Peru. 1044

7 4. Goldscheider, N., Klute, M.,Sturm, S. & Hoetzl,H.,(2000), The Pi method a Gis based approach to mapping groundwater vulnerability with special consideration of karst aquifers- Zeitschriffft Angewandte geologie, 46,3, pp ; Hannover. 5. Hoelting, B., Haertle, T., Hohberger,K-H., Nachtigall, K.H.,Villinger, Weinzerl.,Wrobobel, (1995), Konzept zur emittlung der schutzfunktion der grundwasserue berdeckung-geol. [ translated into English by federal institute foe geosciences and natural resources : concept for the determination of the protective effectiveness of the cover above the groundwater against pollution- working group on hydrogeology, 28p. ;Hannover] 6. Jambor, J.L., (1994), Mineralogy of sulphide-rich tailings and their oxidation products. In: Jambor, J.L. and Blowes, D.W. (eds.): Short Course Handbook on Environmental Geochemistry of Sulphide Mine Waste. Mineralogical Association of Canada, Nepean, 22, pp M. Moustafa, G. Parkin & P. Younger, (2005), Modeling spoil heap heterogeneity and its impact on PRB performance, Fifth International Conference on Calibration and Reliability in Groundwater Modelling from Uncertainty to Decision Making. 8. Margane, A., Hobler, M. & Subah,A.,(1997) : Mapping of groundwater vulnerability and hazard to groundwater in the Irbid area, Northern Jordan- report prepared by WAJ & BGR, technical cooperation project advisory to water authority of Jordan special report No.3, p.50 ;Aman. 9. Nordstrom, D.K. and Alpers, C.N., (1999), Geochemistry of acid mine waste. In: Plumlee, G. S. and Logsdon, M.J. (Eds.), Reviews in Economic Geology, The environmental geochemistry of ore deposits. Part A: Processes, techniques, and health, 6A, pp Singer, P.C. and Stumm, W., (1970), Acid mine drainage: the rate limiting step. Science, 167, pp Thapinta, A. & Hudak, P. F.,(2003), Use of geographic information systems for assessing groundwater pollution potential by pesticides in Central Thailand. Environ. Int. 29, pp Theis, C.V., (1935), The relation between the lowering of the piezometric surface and the rate and duration of discharge of a well using groundwater storage, Am. Geophysical. Union Trans, 16, pp Worrall, F. & Besien T.,(2005), The vulnerability of groundwater to pesticide contamination estimated directly from observations of presence or absence in wells. Journal of Hydrology 303, pp Worrall, F. & Kolpin, D. W., (2004), Aquifer vulnerability to pesticide pollution - combining soil, land-use and aquifer properties with molecular descriptors. J. Hydrology. 293, pp Younger, PL., (2002), Mines of information. Chemistry in Britain, 38 (2), pp