The expansive soil at the top of a soil profile consists of a 4.5 m thick active zone that is subjected to seasonal moisture variations. A shallow foundation is to be placed at 1.5 m depth. Constant volume swell pressure tests were carried out on specimens from different depths of this soil where the swell percentage s_{w (1)} under the overburden and foundation pressures (σ'_o + σ'_s) were measured as follows.

Depth below ground level (m)	Swell percent under overburden + foundation pressure, sw(1) (%)
1.5	5.2
2.5	3.7
3.5	2.1
4.5	0.0

Estimate the total likely swell beneath the foundation.