Hydrogeochemical Assessment of Groundwater Quality inGulshan-e-Iqbal, Karachi, Pakistan

Abstract

Rapid urbanisation and the absence of piped water infrastructure in many districts of
Karachi have increased dependence on shallow groundwater; yet systematic
hydrogeochemical assessments of individual town-level aquifers remain scarce. This study
presents a comprehensive evaluation of groundwater quality in Gulshan-e-Iqbal Town,
District East, Karachi, Pakistan, a densely populated coastal urban area underlain by the
Miocene Gaj and Oligocene Nari Formations. Groundwater samples were collected from
eleven boreholes and hand pumps distributed across the town and analysed for
physicochemical parameters including pH, electrical conductivity (EC), total dissolved
solids (TDS), total hardness, calcium (Ca²⁺), chloride (Cl⁻), and bicarbonate (HCO₃⁻) using
standard titration, spectroscopic, and electrochemical methods. Results were benchmarked
against World Health Organization (WHO) and Pakistan National Environmental Quality
Standards (NEQS) guidelines. EC varied from 0.86 to 2.47 mS/cm, indicating a broad
gradient in dissolved ion concentrations across the sampling sites. Total hardness ranged
from 210.77 to 1176.43 ppm (mean: 646.69 ppm), classifying most groundwater as hard to
very hard, attributable to active carbonate mineral dissolution from the aquifer lithology.
Chloride concentration exceeded the WHO aesthetic guideline of 250 ppm; the spatial
uniformity of this exceedance, combined with the sewage odour recorded at seven sites,
implicates leaking urban sewage infrastructure as the dominant anthropogenic chloride
source. Bicarbonate concentrations (50.97–172.89 ppm) indicate predominantly geogenic
alkalinity generated through CO₂–water–rock interaction along the groundwater flow path.
A strong positive correlation between EC and TDS confirmed the internal consistency of
the dataset, while the dominance of Ca²⁺ in controlling hardness reflects carbonate
weathering as the primary geochemical process. Water Quality Index (WQI) analysis
classified 73% of samples as poor and 18% as very poor, with only one site (S7) meeting
acceptable quality thresholds. The thresholds. The Piper diagram classification identified a
mixed Ca–Na–Cl hydrochemical facies, indicating that groundwater chemistry is
transitioning from natural geogenic control toward anthropogenic and salinity-driven
modification, consistent with coastal urban aquifer degradation. These findings confirm that
the groundwater of Gulshan-e-Iqbal Town is largely unsuitable for direct consumption
without treatment.