Geophysical Survey for Groundwater Development: A Case study of Aero Gardens Estate, Abuja Nigeria

Abstract

Geophysical survey methods are applied in a wide variety of areas.

They are used for oil and mineral prospecting, for solving

groundwater and engineering problems, and in logging. The

geophysical method employed in this study is strictly for

groundwater development. The aim of the geophysical survey is to

locate a suitable point for the drilling of a borehole that will be

capable of meeting the safe water requirement for domestic purposes

and to proffer solutions to the low yield of groundwater encountered

around the survey area. This was actualized with the determination

of the bedrock, determination of the degree of fracturing of the

bedrock, delineation of the various lithological units encountered

during the survey, and lastly, the evaluation of the aquifer potential

of the subsurface. Field method employed for the survey is the

Vertical Electrical Sounding (VES). The geophysical survey

indicates a total weathering profile of 5m underlying the weathered

to fractured granitic basement. This shows that the weathered

overburden is not expected to yield any appreciable quantity of

water to the well due to its shallow nature and high resistivity values.

Water is therefore expected only within the basement which shows

indication of fracturing at depths between forty and seventy meters

(40— 70m). Drilling is recommended on the strength of the presence

of fractures to a minimum depth of 70 meters and an optimum depth

of 80 meters. Point of terminating the well will be at the discretion

of the supervising geologist based on the water yield. However, it is

important to know that accurate water yield of wells are determined

only after the conduct of a pump test to establish the true aquifer

characteristics. Care should also be taken in the design, construction

and completion of the well as poor design and construction may lead

to a reduced well yield and shorter lifespan for the borehole.

Sanitary land fill should be installed at the contact with the basement

to exclude infiltration of surface water into the borehole and also a

cement grout should be placed from 0– 3 meters to ensure maximum

sanitary condition in the vicinity of the borehole. The completed well

is expected to be installed with a submersible pump.