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The Evaluation of Geotechnical Barriers Using Equivalency Calculations L’Évaluation Des Isolants Geotechnique Avec L'utilisation Des Calculations D’Égalité

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The Evaluation of Geotechnical Barriers Using Equivalency Calculations L’Évaluation Des Isolants Geotechnique Avec L'utilisation Des Calculations D’Égalité INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND GEOTECHNICAL ENGINEERING This paper was downloaded from the Online Library of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE). The library is available here: https://www.issmge.org/publications/online-library This is an open-access database that archives thousands of papers published under the Auspices of the ISSMGE and maintained by the Innovation and Development Committee of ISSMGE. The evaluation of geotechnical barriers using equivalency calculations L’évaluation des isolants geotechnique avec l'utilisation des calculations d’égalité I.SzabÔ, B.Kovâcs & I.Horvâth - University of Miskolc, Miskolc, Hungary ABSTRACT: The authors presents the methodology of equivalency calculations of geotechnical barriers and focus on the different behaviour of several GCL brandings and soil-bentionite mixtures during the contaminant transport processes. RÉSUME: Les auteurs present la théorie de la méthode des calculations d’égalité pour les isolants geotechnique avec la prise en consideration de la difference de la caractère des materiux geosynthetique et des sol-bentonite mixtures avant le transport des pollutants. 1 INTRODUCTION regulation is that the wastes are divided into three main groups: municipal wastes, and first and second class hazardous wastes. Liner systems built up from natural or synthetic materials are The required technical barrier depends on thickness and widely used in the environmental engineering both at waste hydraulic conductivity of tOhe subsoil and on the quality of the disposal facilities, both during remedial activities since the waste is to be deposited. All the professional regulatory aspects isolation of different pollution sources is one of the most are discussed in the relevant literature (Szabo & Kovacs, in important issues to avoid extensive contamination in press), that is why here only a short summary is given. environment or to restrict the penetration of hazardous substances into the intact areas. 2.1 Requirements for the subsoil o f the landfill The structure and composition of bottom lining systems, landfill covers and other technical barriers are controlled by acts, For the subsoil the European Council Directive 1999/31/EC technical guidelines or standards. The regulations for compacted is taken into consideration, which requires at least 5 m thick clay liners describe the required mineral compound, compaction, subsoil with the hydraulic conductivity less then 10' 9 m/s for and hydraulic conductivity. Nowadays new lining materials are hazardous wastes and 1 m thick subsoil with the same introduced (s.a. geosynthetic clay liner (GCL), sand-bentonite permeability as above for non-hazardous wastes. If there is no mixtures, clayey polymers, sand and potassium silicate mixtures, natural mineral subsoil barrier having the mentioned quality, etc.) because of their smaller thickness, more homogeneous then an equivalent, built layer from mineral material is suitable. quality, and due to that its relative cheapness in comparison to Depending on the thickness of suitable subsoil and its the traditional compacted clay liner (CCL) systems. permeability determined using laboratory and field tests subsoil The selection of the technically-economically best solution categories are established. and the predestination of the applicability of competitive alternatives is considered using the term equivalency. 2 .2 The regulation o f the liner system structure From regulatory and waste management aspects the easiest way to control the isolation is to define the standard barrier types The structure of the liner system on an area which is qualified to be used for different waste or contaminant species. The as capable for waste disposal must be determined by an recommended standard barrier types, however, may not often be integrated consideration of the natural capabilities of the subsoil implemented in practice because of technical or financial and the hazard potential of the disposable waste. reasons. In these cases only construction of such barriers is The hazard potential of the disposable waste can be allowed which has the same or even higher efficiency in determined: isolation than that of the prescribed ones. The approval of barrier - without any previous examination based on the effective replacement might be completed by means of contaminant decree. The Hungarian decree of hazardous waste transport equivalency calculations. management assigns I-IH. hazardous categories and gives the The paper presents the recently used lining systems in waste list of type of wastes belonging to each of these categories. disposal, shortly describes the Hungarian regulations on the - according to a classification of wastes mto eluate categories mentioned field. It gives a detailed explanation of the theory of based on analytical and ecotoxical test of wastes or extracts calculation of barrier equivalency and efficiency by analytical (eluates). and numerical solutions of the transport equation. To The proposed decree distinguishes three eluate categories demonstrate the problems of equivalency some studies based on similarly to the Austrian regulations. The required level of laboratory measurements are presented. protection - it means the minimal requirements for the structure of the lining system for each landfill construction categories - must be determined upon the category of subsoil and hazard 2 THE HUNGARIAN REGULATION OF WASTE degree of the waste, i.e. the eluate category. DISPOSAL Regulation for the structure of the barrier system on the bottom and the sidewalls are shown in Figure 1. Construction In Hungary, the governmental decree No. 102/1996. controls category No. 1. cannot be seen in the figure because there are no the problem of barriers for waste disposal. The principle of that rules for the lining system, as this category of "wastes" having practically potable water quality leachate. Municipal wastes can 1929 Construction categories However, the sorption process is usually non-linear, therefore the non-linear adsorption isotherms (Freundlich or Langmuir) have to be used to characterize the sorption side process. hi case of special contaminants, the effect of radioactive decay or biodégradation might be significant Consequently, their flux has also significant impact on the net process and neglecting those simultaneous phenomena can deteriorate the reliability of the calculations. The effects of all listed phenomena result in changes of contaminant concentration both in time and space, and it can be mathematically written in the following form, called general as a [»„*_».*• *.7] Drainage layer (k£ lO'u/s) \ / /// //P k Co« pactcd mineral harrier transport-equation: (hydraulic conductivity k < 10*«/») In situ clay/toll R — = ( 1) (¡comemliraoi ( £ 2,0-2.5 *m( a C««Kjktilr Drainage layer or Eeotextilc g2c 52c d2z d2c = D, ) — + + D. Fig. 1. The Hungarian regulation (C5.) and recommendations (C1.-C4.) ' 0XJ + ** dxdy 5x5z 1 dydx ’W ‘ dydz for bottom lining systems of landfills d2c a 2 c d2c S v.c') s f vec'| 5 I dzdx v dzdy 1 dz2 dx. n j dy^ n J dz\ n J be disposed in landfills with the lining system of construction category No. 4., it means a combined barrier system consisting where c is the concentration, Djj are the elements of the of 3 x 20 cm compacted soil layer (k < 1 O'9 m/s), a minimum dispersion matrix, v is the pore velocity of seepage, n is the 2 mm thick geomembrane and a leachate collection system. The porosity, X is the degradation coefficient, R is the rate of disposal of HI. degree hazardous waste is allowed in the landfill retardation, and x, y and z are the axes of the local coordinate with a protection of construction category No. 4. Disposal and system, respectively (Bear & Verruijt, 1987). operation must be separated from that of other municipal wastes. Since our task was to determine the possible concentrations The method of separation is determined in each case by the on the safe side of the barrier, the main goal was to solve either environmental authorities. Regulations require the use of analytically or numerically this transport equation. Taking the construction category No. 5. of Figure 1., when I. and H. degree fact into account that the v seepage velocity is a parameter of the hazardous wastes are disposed. The decree orders the use of transport equation, first the determination of piezometric head double geomembrane with 3 x 20 cm thick clay mineral liners. distribution is required to calculate the seepage velocity field The drainage under the top geomembrane has a monitoring using the Darcy-law. function as well. hi contradiction to the previous regulations the principle of 3.2 Types o f Barrier Equivalency liner equivalency has been composed which of course must be considered not just in case of subsoil substitution, but also when We call ,/i” and ,3 ” barrier systems equivalent if the any mineral liner is substituted by other (e.g., GCL, layers concentrations at the protected side in time are equal presuming improved by waterglass or bentonite, etc.) liners. According to that the hydraulic and the concentration gradients are the same. the decree, the condition of equivalency is that the contaminant This means that the ,J3” being an alternative barrier-system concentration of the leachate, seeping through the substituting might only be used if the calculated concentrations 011 the liner must not be higher than that of the subsoil layer or natural protected side are less than the appropriate values using
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