In more detail, the average values of heavy metal concentrations
in each aquifer were calculated. Fe recorded a higher
level in the upper aquifer than that in the middle and bottom
aquifers while Mn concentrations were distributed evenly in
the three aquifers. With the exception of Mn, the levels of
heavy metals in wastewater are higher than those in mixed
water and groundwater. This may be an indicator of anthropogenic
contribution by heavy metals in the environment of
the study area (Todd, 1980). Hence, it could be proposed that
Khobar and Umm-Arradma aquifers are also free from Mn
and Fe contamination. To some extent, a slight increase in
the level of Fe in the groundwater of Neogen aquifer was
recorded. This may be attributed to a slight enrichment to this
upper aquifer by man-made activities. Contamination of
groundwater with Fe is most probably due to multipurpose
usage of Fe in industrial and domestic activities.