Evaluation of groundwater quality in five (selected) Grama Divisions (GN) of Maharagama urban area using Groundwater Quality Index (WQI)

Abstract

The Maharagama  urban area is located in Colombo district, Western province (79052‟E  –  6050‟N and 79056‟E  -  6053‟N) in Sri Lanka. It carries a high population density about more than 1600 km -2. Groundwater in this area is having a great vulnerability for pollution by anthropogenic activities such as excessive use of fertilizers and unregulated garbage dumping directly impact on ground water quality. The present study was carried out to study some important water quality parameters, to evaluate the quality of groundwater in the area using a Water Quality Index (WQI) and to compare the water quality between Grama Niladari (GN) divisions in the study area. Five GN divisions (Jambugasmulla, Gangodawila south B, Wijerama, Navinna and Wattegedara) in Maharagama urban area were selected and the study and fifty five wells were sampled once in three months for a period of nine month from November 2010 to July2011. Physico-chemical and microbiological parameters were measured and WQI was calculated for each well using twelve physico-chemical parameters including total alkalinity, hardness, conductivity, pH, chloride, nitrate, total phosphate and five heavy metals (Cd, Cu, Zn, Fe and Pb). First, a weight value was assigned for each of the twelve parameters depending on their relative importance. The maximum weight (5) has been assigned to parameters with major importance. The SLSI drinking water standards were used as a reference in calculations. Water quality classification based on WQI value of 50-100, 100-200, 200-300, >300 reference  to excellent, good, poor, very poor and water unsuitable for drinking respectively. Microbiology parameters were considered separately. The resulted WQI values in groundwater ranged from 17.08 to 280.91. The results revealed that the water quality of the  wells deviate from excellent to very poor quality. The nitrate concentration of some wells exceed more than >45mg/l and other physic-chemical parameters remained with the SLS water quality standards. Considering all the water quality parameters, the poorest water quality was recorded in Navinna GN division where located around Navinna garbage dumping site. Almost all tested dug wells were contaminated with fecal coliform and E. coli. In certain wells the fecal coliform counts were exceeded more than1100/100ml. It was observed that unregulated garbage dumping, uncontrolled application of organic and inorganic fertilizers, constructing toilet pits very close to wells and increasing human settlements in the study area positively effect on poor ground water quality of the area.

Key words: ground water quality, nitrate, E.coli, anthropological activity