ABSTRACT
According to the Safe Drinking Water Act Underground Injection Control (UIC) Program an injection well is any bored, drilled or driven shaft, or a dug hole where the depth is greater than the largest surface dimension, that is used to discharge fluids underground. The extent of groundwater contamination arising from the use of injection wells was carried out to examine the physico-chemical, microbial and trace metals status in Government Reserved Area, Edo State. Twenty (20) samples were collected, which include seventeen (17) pumping borehole samples and three (3) injection wells samples, were analyzed for physico-chemical properties using atomic absorption spectrometer (AAS) modern 969 unicam series. The result of analysis was then subjected to statistical treatment, Spearman’s Correlation Coefficient, descriptive statistics to ascertain significant difference among the trace metals association and status of contamination/pollution respectively. The correlation result between the analyzed parameters in the injection well and borehole sample, revealed positive correlation coefficient at r (0.01) and r (0.05) indicating strong association between them, which probably reflects their related source of contaminations. However, correlation was also not significant among some parameters in the groundwater samples indicating an uncommon source of contamination. Result from the analysis showed that both groundwater and injection well samples in the study area are slightly acidic with pH values ranging from (5.1 – 6.4) respectively. The extent of trace metal contamination in the injection wells are as follows: Lead; (1.12 -1.5mg/l), Iron; (0.34-2.15mg/l), Copper; (0.16-4.04mg/l), Chromium; (0.11-0.21mg/l), Zinc; (3.14 -4.22mg/l), Cadmium (0.02mg/l), Manganese; (0.32-0.65mg/l), Nickel; (0.46 -1.10mg/l), while presumptive Coliform count range from (1.8 x 104 – 2.2 x 104), E-coli count (3.3 x 101 – 4.8 x 101). While for the borehole samples most of the parameters analyzed for, falls within the World Health Organization (WHO) and Nigerian Standard for Drinking Water Quality (NSDWQ) standard apart from trace of heavy metal such as Nickel (0.24mg/l and 0.26mg/l) in borehole (BH16 and BH5) and Chromium (0.1mg/l) in borehole (BH3 and BH15) respectively, and the presence of presumptive Coliform count ranging from (3.6 x 102 – 2.1 x 104). The presence of both elements are harmful to human beings when ingested. Also, the borehole that are not close to the injection wells do not have trace of heavy metals which further reveals that as one moves away from the injection well contamination of groundwater is not obvious, Further more the use of injection wells for controlling flood is a possible source of groundwater contamination which can lead to possible pollution if not stopped.
