Chemical and Microbiological Analysis of Groundwater After a Major Flood Event in Darna City

Abstract

This study evaluates the impact of severe flooding caused by Storm Daniel on groundwater quality in Derna city. Groundwater samples from five wells were collected immediately after the flood and analyzed for physical, chemical, and microbiological parameters. Wells 1 and 2 were located within the flooded area, while Wells 3, 4, and 5 were nearby but were not submerged.
The results indicate that the pH values of groundwater samples ranged from 7.17 to 7.61, remaining within the permissible limits set by both national (Libyan standards, 2008) and international (WHO guidelines, 2003) water quality standards.
Total Dissolved Solids (TDS) levels were generally within acceptable limits, except in Wells 1 and 2. The highest TDS concentration was recorded in Well 2 at 1837 mg/L, followed by 1147 mg/L in Well 1.
Electrical Conductivity (EC) values exceeded the permissible limit of 1400 µS/cm in several wells. The highest EC value was recorded in Well 2 at 3675 µS/cm.
The concentrations of cations (Mg²⁺, Ca²⁺, and Na⁺) were mostly within allowable limits. However, sodium levels exceeded the standards in some samples. Among anions, sulfate (SO₄²⁻) and chloride (Cl⁻) concentrations were notably elevated, especially in Wells 1 and 2, exceeding both national and international permissible limits.
The total bacterial count per milliliter detected in the well water revealed the presence of bacteria in Wells 1 and 2. Notably, water from these wells was found to be unfit for drinking.