The prime necessity for soil quality assessment using ultra wideband (UWB) radars is to characterize the soil layers with varying dielectric properties. Pre-requisite for such scenarios is determining soil layer boundaries and their respective dielectric properties. Towards that attempt, for the first time, this work introduces a technique to calculate the anterior and posterior boundary of a dielectric medium, with the help of a single monostatic UWB radar. Since soil consists of a large proportion of water with electrolyte, we validate our technique via experiments on potable water and salty water. The root mean squared error for anterior and posterior boundary detection is less than 0.13m and 0.40 m, respectively.