Pollution Research Paper

CHARACTERIZATION OF GROUNDWATER QUALITY IN THEHARD ROCK AQUIFERS OF TRIVANDRUM DISTRICT,KERALA, INDIA

PRATHIBHA RAVEENDRAN, E. SHAJI* AND S. K. SHAMNA

Abstract

Groundwater quality of the hard rock aquifers of Trivandrum district and its suitability fordomestic purposes has been examined. Twenty nine groundwater samples from bore wells werecollected from the study area and major and trace element hydrochemistry was determined. Thegroundwater samples show slightly acidic nature with pH ranges between 5.06 and 8.21. ElectricalConductivity (EC=98 - 433 μS), TDS (70.7 – 273.4 ppm), calcium (0 – 28 ppm), magnesium (1.2 – 21ppm) and chloride (30 – 97.6 ppm) are within the desirable limit except only one sample fromParassala (EC = 1271 μS, TDS = 778.5 ppm, Ca = 110.2 ppm, Mg = 38.7 ppm, Cl=365 ppm). Sodium(10 – 98 ppm) and potassium (1 – 10 ppm), bicarbonate (5 - 80 ppm), sulphate (0 – 76.7 ppm),phosphate (0 – 0.4 ppm) and nitrate (0 – 0.251 ppm) are within the permissible limit in all thesamples. Sodium, potassium and chloride could be derived from feldspars and mafic mineralspresent in the khondalites of the study area. Trace elements were determined using AAS technique.40% of the samples have a high value of iron which exceeds the maximum permissible limit. Highconcentration of iron in the groundwater is contributed by the mineral garnet which is present inthe garnetiferous biotite gneiss. The concentration of iron in the study area ranges from 0 to 3.388ppm. Samples from Malayinkeezhu, Parassala, Vilappilsala and Nedumangad show highconcentration of cadmium and the bore wells of these areas tap water from the fracturedgarnetiferous biotite gneiss rock. The concentration of cadmium, ranges from 0 to 0.053 ppm, maybe derived from the hard rock or from the runoff from the waste dumping cites (eg: Vilappilsala)and pesticides used in the agricultural areas. The concentration of lead above the maximumpermissible limit in 40% of the samples and its concentration is ranges from 0 and 0.157 ppm.Similarly high concentration of nickel is reported from 60% of the samples and it ranges from 0 to0.204 ppm. High concentration of lead and nickel may be attributed to the K-feldspar andmetamorphic rocks present in the study area. Manganese and copper are within the permissiblelimit in all the samples. Piper diagram shows that most of the groundwater samples belong to Ca-Cl type. The quality of the groundwater in the bore wells is, in general, good. However, this studyreports the high concentration of trace elements in groundwater of hard rock aquifers, which maybe due to the chemical weathering of metamorphic rocks, rock water interaction and long residencetime of groundwater in the zone.