Azura-Edo Independent Power Plant Environmental Impact ... - IFC

4.4 GEOLOGY
The Study Area is located within the Niger-Delta Basin and Benin formation
and along with Edo State is geologically characterized by deposits laid during
the tertiary and cretaceous periods (Alile, Molindo and Nwachokor, 2007). The
Benin Formation has been created from weathered sedimentary rock (Aziegbe,
2006). The Niger Delta Basin is one of the sedimentary basins in Nigeria that
derives from weathered and eroded materials of Precambrian basement
complex rocks of the South-Western part of Nigeria (NIPP, 2010).
The Benin Formation comprises unconsolidated iron oxide-rich sands with
alternating beds of shale, clay and sandy clay. The sands range from fine to
medium and in places demonstrate coal lignite streaks and wood fragments.
The formation is covered with loose brownish sand (quaternary drift)
varying in thickness and is about 800 m thick; almost all of which is water
bearing with water level varying from about 20 m to 52 m. It is generally
believed to be highly permeable, porous and prolific in water yield. The aquifer
yields range from 28.4 m 3 hr-1 at Iyanomo (south of the City), 125 m 3 hr-1at
Uselu (central part) to 208 m 3 hr-1 at Ogba (northern part) with a draw down
ranging from 4.8 m at Iyanomo, 1.8 m at Uselu to 6.7 m at OgbaDue to the
estimated rainfall for Benin City of over 2000 mm per annum (Erah, Akujieze
and Oteze, 2002)
The upper layer of the Benin formation is composed of iron-rich red earth
derived from iron-stained fragmented parent rock (NIPP, 2010) and derives
from the Oligocene era.
4.5 SOILS
Soil sampling was conducted at nine locations during the dry season in the
Study Area (including areas to the south and west of the proposed plant
location) and at nine locations during the wet season (Figure 4.3). The sampling
locations with latitude and longitude coordinates for all biophysical variables
measured are included in Annex B.
All core soil samples were taken at two depth intervals (0 - 15cm of topsoil and
15 - 30cm of subsoil) using a stainless steel auger. The soil samples were then
stored in plastic buckets, and homogenised before sub-sampling. The sub-soil
samples were subsequently stored on ice (below 4 º C) and transported to
Searchgate Laboratories. The soil samples were analysed according to their
physico-chemical, heavy metals, oil and grease, hydrocarbons, and
microbiological properties. Soils were also analysed on site for colour, texture
and moisture content. Soil analysis results are outlined below, and full
laboratory results are provided in (Annex B).
AZURA EDO IPP
4-6
DRAFT EIA REPORT