An examination of the relative dissolution of two gravels in acetic acid and impact on leachate collection system performance

P.T. Saheli, R.K. Rowe, F. Gondim, B. Forrestal

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Geoenvironmental Engineering

ABSTRACT: The potential dissolution of two different types of carbonate based gravels (Michigan gravel with 98% dolomite and Beachville gravel with 47% dolomite) in acetic acid solution (pH5) is examined at 40°C and room temperature. During the two-month experiment, Michigan gravel lost 0.5 % mass at room temperature (corresponds to 3.2% mass loss per year) and 3.6 - 3.7 % mass at 40°C (23% per year). For Beachville gravel the mass losses were 0.8-1.0 % at room temperature (5.8%/year) and 3.4-4.1% at 40°C (22-26%/year). With increasing pH or temperature, calcite solubility decreases which leads to increase in precipitation. The design implications of stones with a wide range of calcite levels (0 and 31.7%) on leachate collection system performance were reviewed. It is expected that a landfill drainage layer built with the Michigan stone will have lower clogging rate and longer service life. RÉSUMÉ Le potentiel de dissolution de deux types différents de graviers à base de carbonate (gravier du Michigan avec 98% de dolomite et gravier de Beachville avec 47% de dolomite) dans une solution d'acide acétique (pH5). Au cours des deux mois d'expérience le gravier du Michigan a perdu 0.5 % de sa masse à température ambiante et entre 3.6 et 3.7 % de sa masse à 40°C. Pour le gravier de Beachville les pertes de masse étaient de 0.8 à 1.0 % à température ambiante (5.8% par an) et de 3.4 à 4.1 % à 40°C (de 22 à 26% par an). Avec l'augmentation du pH ou de la température la solubilité de la calcite diminue ce qui conduit à l'augmentation de la précipitation. Il est anticipé qu'une couche de drainage d'enfouissement construite avec de la pierre du Michigan aura moins tendance à se boucher et aura une durée de vie plus longue. 1 INTRODUCTION Modern engineered landfills require a barrier system to minimize the migration of contaminants into the groundwater system. One component of barrier systems is leachate collection system which controls the leachate head and reduces the potential advective transport of contaminants though the liner system (Rowe et al. 2004). According to the Ont. Reg. 232/98, 'the primary leachate collection system should consist of perforated collection pipes bedded in a layer of stones which must have a D85 of not less than 37 millimetres, a D10 of not less than 19 millimetres, a uniformity coefficient (D60/D10) of less than 2.0, and, when measured by weight, not more than 1.0 per cent of the stones may pass the US #200 sieve'. This initial grain size of the leachate collection system may change with time due to various factors including interaction between leachate and gravel. Bennett et al. (2000) examined the stability of calcium-containing aggregates as drainage material in landfill leachate collection system. They concluded that under the examined condition, dissolution of dolomite in landfill leachate is not significant. In this study, dolomite and calcite dissolution from two carbonate based gravels in acetic acid solution (pH5) were monitored for two months and their mass losses were calculated. 2 GRAVEL EXAMINED Two different types of crushed limestone, from two different locations, were examined. The two limestone gravel samples will be referred to herein as Michigan gravel and Beachville gravel. They had mineralogy as indicated in Table 1. Both gravels had a grading in accordance with Ontario Regulation 232 requirements. For each gravel type, three different sizes of stones (large, medium, small) were selected for testing. An effort was made to select stones with similar shapes and sizes (and hence surface area for exposure to the acid). The average weight of each type of stone was 70g, 30g and 17g for large, medium and small stones respectively. The average sizes were 5cm×4cm×3cm (large), 4cm×3cm×2cm (medium) and 3cm×2cm×2cm (small) for Michigan samples and 5cm×3cm×3cm (large), 3cm×3cm×2cm (medium) and 3cm×2cm×2cm (small) for Beachville samples. The stones were washed with deionized (DI) water to remove dust and loose particles and then air dried and weighted. The weight of each stone

RÉSUMÉ: amination of the relative dissolution of two gravels in acetic acid and impact on

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P.T. Saheli; R.K. Rowe; F. Gondim; B. Forrestal (2014) An examination of the relative dissolution of two gravels in acetic acid and impact on leachate collection system performance in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper359,author = P.T. Saheli; R.K. Rowe; F. Gondim; B. Forrestal,title = An examination of the relative dissolution of two gravels in acetic acid and impact on leachate collection system performance,year = 2014}