We engaged Tasology to produce a soil permeability map for a 12-hectare municipal retention basin in the Ikeja district. The first month of data collection and analysis gave us a clear picture of the subsurface conditions. The double-ring infiltrometer tests across 18 points revealed hydraulic conductivity values ranging from 0.3 to 1.1 m/day, with the lateritic clay layers showing the lowest permeability. This directly informed the basin's liner design and the placement of the underdrain system.
The preliminary report included a comparison against the Water Resources Act guidelines for stormwater retention. The team flagged two test points where the measured infiltration rate fell below the 0.5 m/day threshold for unlined basins. That finding saved us from a potential compliance issue during the environmental impact assessment. The mapping also identified a shallow perched water table in the southwestern corner, which we had not anticipated from the borehole logs alone.
What stood out was the specificity of the deliverables. The permeability contours were plotted at 0.2 m/day intervals, and the report included a table of recommended retention volumes per sub-catchment based on the measured soil data. No generic recommendations—just numbers tied to our site. The communication was direct: weekly email updates with the raw field data and a short note on what the numbers meant. No jargon for the sake of it.
After one month, we have a working model of the site's drainage behavior. The next step is to run the 10-year and 25-year storm simulations using the permeability map as input. I expect the final design to require a 15% larger detention volume than the initial estimate, based on the lower-than-expected permeability in the central zone. That is a concrete adjustment we can budget for now, rather than discovering it during construction.