Ajdanlijsky G. et al. FLUVIAL ARCHITECTURE OF THE SEDIMENTARY … 50 years University of Mining and Geology “St. Ivan Rilski” Annual, vol. 46, Part I, Geology and Geophysics, Sofia, 2003, pp.1-6 FLUVIAL ARCHITECTURE OF THE SEDIMENTARY AQUIFER COMPLEX IN THE AREA OF SANITARY LANDFILL PLOVDIV George Ajdanlijsky (1) , Nikolay Stoyanov (2) University of Mining and Geology “St. Ivan Rilski”, Sofia 1700, Bulgaria E-mail: ajdansky@mgu.bg (1) , nts@mgu.bg (2) ABSTRACT Aim of the study is to development a lithofacial and fluvial-architectural model of the deposits from the area of the sanitary landfill Plovdiv, which to allow the compila- tion of a reliable mathematical model for estimation and prognoses of the range and the scale of ground water contamination as result of the landfill exploitation. The developed sedimentological and stratigraphical models are based on field, borehole and geophysical data. Based of field studies and the available subsurface data in the area fluvial lithofacial types were defined and detail lithofacial profiles were developed. This allowed the revealing of the channel, the near-channel and the overb- ank fines deposits, the characterization of their architecture and determination of four elementary fluvial cycles (EFC). From the obtained 2-D lithofacial data and the information about the direction of the fluvial paleotransport 3-D architectural elements are defined, which further are differentiated according to their hydraulic proper- ties. Three basic units for the hydrogeological model are defined and identified - high-permeable and low-permeable water-bearing bodies and impermeable bodies (aquit- ards), and are localized zones of direct hydraulic connection between the high-permeable beds from different EFC. INTRODUCTION The Neogen-Quaternary aquifer complex in the area of the sanitary landfill Plovdiv is formed in fluvial gravels, sands and mud. The summary thickness of these sediments not exceed 40-50 m (Мерачев и др., 1982). The bedrock is from Upper Cretaceous granodiorite porphyrites which build up the lower aquiclude of this aquifer structure. The wide spectrum of lithological and facial variety of the sediments where the aquifer complex is formed predetermines the wide heterogeneity of conditions that control the pollutant migration. That is why, it is more appropriate to apply the sedi- mentological approach in describing the spatial parameters of 3D bodies from the complex with homogeneous hydraulic char- acteristics (aquifers and aquitard), rather than the standard model of “multiple aquifer complex”. MATERIAL AND METHODS For achievement of relevant of the fluvial architecture model, sequences of outcrops, situated transversally and longitudin- ally to the dominating directions of sedimentary paleotransport were studied and were carefully correlated. The collected field lithofacial data and the data from all drilled in the area the san- itary landfill exploration boreholes (Fig. 1) allowed the definition of 14 fluvial lithofacieses. For revealing the spatial distribution and interrelations of the determinated lithofacieses, a set of lithofacial profiles embraces the area of the sanitary landfill is developed. Based of the spatial interrelations and the genetic interpretation of the established lithofacieses, the systematic measurement of all type indicators of the direction of the sedi- mentary paleotransport and after the detailed study of the mor- phology and the orientation of the bounding surfaces of the es- tablished lithofacial units, three fluvial architectural-element elements were distinguished. The lithofacial and architectural- element schemes, as well as the nomenclature of the bounding surfaces order proposed by Miall (1996) were accepted. Be- cause of the nature of the existing lithological data, some modi- fications in the architectural-element nomenclature are made. The spatial distribution and interrelations of the architectural- element units define several elementary fluvial cycles (EFC) situated one above other. The base of every separate EFC is 5 -th order erosion surface. They correspond to the connotation of the described by Janev (Янев, 1982, p. 70) elementary sedi- mentary cycles. As a complex of genetically connected and regularly replaced lithofacieses EFC correspond to the first or- der cycles (elementary cycles) described by Logvinenko (Логвиненко и др., 1976, p. 123). The proposed by Folk et al. (1970) criteria for definition of the gravel lithofacial units are accepted. According to them, the presence of 30% or more gravel clasts (coarser than 2 mm) is accepted as lower limiting value of this group. Matrix-supported and grain-supported gravel lithofacies varieties are distinguish. The lithofacial units (as well as for the constructed by them architectural elements) are defined according to their hydraulic properties on the base of grain size data (using φ-scale) re- ceived from studies of representative samples. The proposed by Friedman (in Friedman et al.,1992, p. 36) seven-step scale for estimation of the degree of sorting of the sediments is applied. The results are presented as I(σ)/Ski (standard deviation/skewness) diagram (Fig. 2). ANNUAL University of Mining and Geology “St. Ivan Rilski”, vol. 46 (2003), part I GEOLOGY AND GEOPHYSICS 1