5.1.3. Characteristics of the water-bearing zone
There are found a vast difference between hydrogeological conditions in
other areas from the coastal region of Bangladesh. The main aquifer
transmissivity on coastal aquifer have found the ranges from 250
m2/day to 10000 m2/day with the
average value of 1000 m2/day. Generally, the aquifer
storage capacity has increased with depth with the grain size of aquifer
materials increase. It has indicated by the authors (Bakhtine &
Industry, 1966; Zakaria et al., 2015), the thickness of water-bearing in
the different depth of the study area and actual hydrogeology has
considered as complex in nature. From Fig. 2(a), hydro stratigraphic
(Table 2) sections has been divided into five lithologic part with the
correlation of two wells: (a) sandstone and topsoil, (b) clay stone
zone, (c) sandstone with clay (d) shale (siltstone and clay) and last
(e) sandstone. The main water aquifer zone has found in the Early
Miocene age and the formation of Middle Boka Bil (Fig. 3(A)). The
lithologic responses of the resistivity log (35.6-42.7) oh-m. The cross
of the actual water-bearing zone section of the two different wells has
been divided depend on their hydro stratigraphic unit. According to the
water-bearing condition, the aquifer geometry of the lithologic
characteristics has divided into 4 parts on the top to bottom Fig. 4
(A): (1) water table (2) aquiclude (3) aquitard (4) aquifer. From the
lithological analysis of individual logs (resistivity and SP log) of the
cross-section has been indicated the aquifer on the Middle Boka Bil
(Early Miocene age) on 184m to 244m depth and it has considered the main
aquifer zone of safe groundwater.