Centrifugal modeling of leaking underground storage tanks

Leaking underground storage tanks (UST) and contaminated soil must be removed to comply with environmental regulations. A major problem associated with removal of contaminated soils is the lack of a proven method to determine the extent of soil contamination. The movement of chemicals and the subsequent fate and transport of chemicals from the leaking UST are often estimated from field explorations coupled with mathematical models. A major difficulty in these modeling efforts has been a lack of information concerning the constitutive relationships governing multi-phase contaminant movement. Centrifugal modeling coupled with field investigation is an alternative way of simulating and estimating chemical movement and transport through soils. In centrifugal modeling an actual three-dimensional profile is created and the centrifuge, because of scaling laws, accelerates the chemical flow and transport processes such that a field event that lasts decades is simulated within hours or days. The centrifugal modeling technique was used to simulate the movement of gasoline through the vadose zone from leaky UST and to study the distribution of various constituents of gasoline. The results show that for granular soils the movement of gasoline was advective and the free product formed a pool on top of the water table directly below the UST. However, for fine grained soils, instead of the pooling of free products, spreading of components of gasoline at different rates was observed to be due to the movement and subsequent transport of gasoline in anisotropic soils.