Abstract—The lignite-fired power plants in the Western Macedonia Lignite Center produce more than 8 ⋅ 10 6 t of fly ash per year. Approximately 90% of this quantity is used for restoration- reclamation of exhausted open-cast lignite mines and slope stabilization of the overburden. The purpose of this work is to evaluate the environmental behavior of the mixture of waste rock and fly ash that is being used in the external deposition site of the South Field lignite mine. For this reason, a borehole was made within the site and 86 samples were taken and subjected to chemical analyses and leaching tests. The results showed very limited leaching of trace elements and heavy metals from this mixture. Moreover, when compared to the limit values set for waste acceptable in inert waste landfills, only few excesses were observed, indicating only minor risk for groundwater pollution. However, due to the complexity of both the leaching process and the contaminant pathway, more boreholes and analyses should be made in nearby locations and a systematic groundwater monitoring program should be implemented both downstream and within the external deposition site. Keywords—Co-deposition, fly ash, leaching tests, lignite, waste rock. I. INTRODUCTION HE lignite basin of Kozani – Ptolemaida – Amyntaio is the biggest and most important in Greece. The proved lignite reserves contained in this basin are more than 4·10 9 t, which account for 65–70% of the country’s total coal resources [1]. There are 5 lignite mines currently in operation in this area that feed 4 thermal power plants (TPPs). These plants have a total installed capacity of 4000 MW and cover 32% of the total energy generation in Greece. As a consequence of lignite burning, large quantities of fly ash are produced. In the Western Macedonia Lignite Center (WMLC), the annual quantities of fly ash exceed 8·10 6 t [2]. Over 90% of this fly ash is used in exhausted open-cast lignite mines restoration-reclamation with overburden. Fly ash acts as binder for the increase of slope stabilization of the overburden in the restoration process. Several studies have been conducted on Greek fly ashes regarding their mineralogical and chemical composition [3]– Dr. A. Mavrikos is with the School of Mining and Metallurgical Engineering, National Technical University of Athens, Athens, 15780, Greece (phone: +30 2107722190; e-mail: mavrikos@metal.ntua.gr). Dr. N. Petsas and E. Kaltsi were with the Generation Environment Department of Public Power Corporation S.A., Athens, 10432, Greece (e- mail: n.petsas@dei.com.gr, e.kaltsi@dei.com.gr). Prof. D. Kaliampakos is with the School of Mining and Metallurgical Engineering, National Technical University of Athens, Athens, 15780, Greece (phone: +30 2107722211; e-mail: dkal@central.ntua.gr). [5], leaching behavior of trace elements and heavy metals [6], [7], as well as the correlation of trace elements and heavy metals in the lignite with the respective compositions in fly ash [8]. However, there are not any available data on the environmental behavior of mixtures of waste rock material and fly ash that are being used for the restoration of open-cast mines. Therefore, the present study deals with the evaluation of the environmental behavior of the co-deposited waste rock and fly ash based on chemical composition and leaching potential tests. For this purpose, a large number of samples were collected from the external deposition site in the South Field mine. The site contains materials with a wide variety of composition (marl, sandy marl, sand, clay etc.), granulometry and stratigraphic origin due to the exploitation of the mine, as well as fly ash from the TPP Agios Dimitrios. II. FLY ASH AND ENVIRONMENTAL INFLUENCE FROM BACKFILLING OPERATIONS A. Fly Ash Fly ash is a fine powder, consisted mainly of spherical, glassy particles that originate from burning of pulverized coal [9]. According to the European standard ΕΝ 197-1, fly ash is divided into two main categories, i.e. siliceous fly ash (V), which contains less than 10% CaO, and calcareous fly ash (W), which contains 10–35% CaO. Siliceous fly ash has pozzolanic properties, while calcareous fly ash may also have hydraulic properties. The American standard ASTM C 618 classifies fly ash into three Classes, namely Class N, which includes raw pozzolans, with a minimum of 70% of SiO 2 +Al 2 O 3 +Fe 2 O 3 , Class F, which originates from anthracite and bituminous coals, with a minimum of 70% of SiO 2 +Al 2 O 3 +Fe 2 O 3 and Class C, which originates from sub-bituminous and lignite coals, with 50– 70% SiO 2 +Al 2 O 3 +Fe 2 O 3 . Class F fly ash usually has less than 5% CaO, while Class C fly ash has a higher CaO content (10– 35%). Greek fly ash in the WMLC is calcareous (W) according to EN 197-1 and Class C according to ASTM C 618, due to its high CaO levels (Table I) [5]. Fly ashes also contain trace elements (As, Pb, Cr, Ni, Zn, Cu, Ba, Th, Se, Mo, etc.) in relatively high concentrations. Table II shows the main trace elements of fly ash in the WMLC [7]. Environmental concerns from the presence of trace Evaluation of the Environmental Risk from the Co-Deposition of Waste Rock Material and Fly Ash A. Mavrikos, N. Petsas, E. Kaltsi, D. Kaliampakos T World Academy of Science, Engineering and Technology International Journal of Environmental and Ecological Engineering Vol:8, No:6, 2014 385 International Scholarly and Scientific Research & Innovation 8(6) 2014 scholar.waset.org/1307-6892/9998419 International Science Index, Environmental and Ecological Engineering Vol:8, No:6, 2014 waset.org/Publication/9998419