Geochemistry of the seepage water from drain hole 0+53 Down, Adit RAA-2 of Tarbela Dam

Abstract

Geochemical parameters of the seepage water from drain hole 0+53 Down, Adit RAA-2 of Tarbela Dam are markedly in contrast with the similar Parameters of the reservoir water. TDS and EC values are significantly higher and the amount of dissolved oxygen is lower in the drain hole seepage water than those of the reservoir water. The data suggest addition of soluble salts from the rocks of the right abutment into the seepage water while in transit from reservoir to drain hole. This clearly shows removal of soluble material from the country rocks and thus creation of voids in the right abutment. Lower values of dissolved oxygen in seepage water, as compared to those of reservoir water, indicate its consumption for the oxidation of ferruginous minerals during the transit period. Both gypsum and limestone are present in the country rocks with the former having higher oxidation potential and thus considered a preferred target of removal through dissolution, as compared to the latter. Therefore, proper future monitoring of the geochemical parameters of the seepage water in various drains is very important for evaluating the geotechnical hazards being posed by the dissolution of gypsum from the country rocks of right abutment of Tarbela Dam.