BOREHOLE PROFILES AND BOREHOLE WATER QUALITY AT THE LAGOS FREE TRADE ZONE, NIGERIA

Dangote refinery

Borehole Descriptions

The studied boreholes were constructed by Efficacy Construction Company. The project area, Lekki Free Trade Zone, Lagos State falls entirely in the Dahomey Basin. The Geology of the area is underlain by sedimentary rocks with no basement outcrop. Conductor casing was installed from surface to 40ft using 400mm casing followed by cementation of the annulus space between the casing and the drilled hole. Borehole was logged and cased to the desired bottom for each borehole point. Backwashing, gravel packing and cementation of fresh water aquifer was done.

Sampling

The samples were collected from five (5) boreholes located within the Dangote Oil Refinery. The samples were collected in sterilized one (1) liter plastic bottles labelled appropriately. Three samples were collected from each of the five borehole points. The samples were stored and transported in a thermally insulated box to the department of Civil and Environmental Engineering, University of Lagos for the physicochemical and microbiological testing.

Physicochemical Tests.

The water samples were tested in the laboratory to determine the physical and chemical properties. The physical properties tested includes Appearance, Color, Odor, pH (was tested at 20OC), Turbidity (FTU), Conductivity (µScm-1), Total Solids (mg/l), and Dissolved Solids (mg/l). The temperature was checked onsite with a pocket Celsius reading thermometer.

The chemical properties tested include Acidity –P (mg/l CaCo3), Alkalinity –M (mg/l CaCo3), Total Hardness (mg/l CaCo3), Calcium Hardness (mg/l CaCo3), Chloride Cl- (mg/l), Sulphite, SO32- (mg/l), Sulphate, SO42- (mg/l), Total Chlorine (mg/l), Nitrite NO2- (mg/l), Nitrate NO3- (mg/l), Ammonia (mg/l), Silica SiO2 (mg/l), Phosphate PO43- (mg/l), Iron Fe2+ (mg/l), Copper Cu (mg/l), Manganese Mn (mg/l), Zinc Zn (mg/l), Lead Pb (mg/l), Arsenic As (mg/l), Mercury Hg (mg/l), Dissolved Oxygen DO (mg/l).

Microbiological Tests
The water samples were tested in the laboratory to check for total bacteria and total coliform. The tests were carried out in accordance with the Institute of Public Analysts of Nigeria (IPAN) decree 100 of 1992, now IPAN Act Cap 1.16LFN 2000. The mean values and standard deviation was calculated for the recorded data for the three water samples for each of the borehole points. The results were compared to the WHO standard for drinking water quality.

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