Petroleum releases from leaking underground storage tanks (LUSTs) pose numerous potential threats to human health and the environment. Petroleum can seep into and through the soil to the water table. At the water table, these liquids can accumulate as a pool on top of the water because most substances in underground storage tanks (USTs) (e.g., petroleum) are less dense than water. Here the chemicals can dissolve into and contaminate ground water and surface water. In Idaho, ground water supplies about 95% of the population's drinking water, so keeping it clean is a high priority. In addition, vapors from petroleum releases can be a health and safety concern within buildings and around construction workers.