Estimating Residual Oil Volume in a Soil
OILVOL estimates the free hydrocarbon volume in a soil and computes the volume of residual NAPL in the saturated and unsaturated zones. To obtain these values, the user enters the depth to air-oil and oil-water interfaces measured in monitoring wells, van Genuchten soil moisture retention parameters (which can be estimated with SOILPARA) and fluid properties. Three-phase constitutive relations are used to obtain the vertical distribution of fluid saturations which are integrated in OILVOL to compute the free product (true product) volume in the soil. OILVOL can also estimate the residual oil volume in the unsaturated and saturated zones after oil skimming. When fluctuations in the fluid tables (air-oil, oil-water) are high, as those resulting from the operation of water and oil recovery wells, and/or when regional ground-water gradients are high and hydrogeology is complex, we recommend the use of the MARS model which estimates transient areal migration, LNAPL/water recovery, and free and trapped NAPL volumes in the vadose/saturated zones.