Hydrochemical response of groundwater to seasonal rainfall-induced deep percolation around a dumpsite

Groundwater quality for wet and dry seasons around an active dumpsite in Aluu, Port Harcourt, was evaluated using a combination of pollution indices, microbial count, and statistical models. Water samples were collected and analyzed for physicochemical and microbial parameters using standard methods. Dilution factor (DF) and correlation heatmap were used to synthesize the source of the contamination while heavy metal pollution Index (HPI) and Nemerow comprehensive pollution index (CPI_Nemerow) were used to evaluate magnitude of groundwater contamination. Results show that electrical conductivity, total hardness, magnesium, lead, cadmium, and total heterotrophic bacteria (THB) exceeded the Nigeria Standard for Drinking Water Quality allowable limits for both seasons. The HPI values for the dry (476.76) and wet (3849.4) seasons and the CPI_Nemerow values for the dry (31.69) and wet (107.37) seasons greatly exceeding the critical values of 100 and 3 respectively. THB counts were also high, however a drop in count occurred from 2.8 × 10³ CFU/mL during the dry to 3.2× 10² CFU/mL during the wet season. An indication that the effect of rainfall on groundwater quality is different for chemical and microbial parameters. While for chemical contaminants, rainfall enhanced mobilization, for microbes rainfall enhanced dilution. The correlation heatmap and the DF showcased the measured parameters in two distinct categories based on hydrochemical control and contaminant source. The study concludes that groundwater from the study area is severely polluted and unsuitable for domestic or agricultural use without advanced treatment.