As members of the Billerica Fire Department surveyed the remains of the Silvas' house on the day after the fire, they discovered an additional casualty of the blaze: the 275-gallon fuel oil storage tank. The fire's heat and falling debris had apparently damaged the oil tank's piping, allowing oil to leak out into the basement. The oil that did not burn in the fire formed a sheen on top of the thousands of gallons of fire-fighting water that had pooled in the basement. Overnight, the oil and water seeped out of the basement, soaking the soil and threatening the groundwater beneath the house. Of particular concern was the fact that the Silvas' drinking water well was located directly adjacent to their house. Nevertheless, the leak was not as devastating as some can be. The volume of oil released was minimal as much of the oil had burned in the fire. The contamination was accessible, allowing for rapid cleanup. Finally, because of the circumstances of the release, the cost of the cleanup was covered by the Silvas' insurance. Oil releases from residential storage tanks can often be catastrophic and, unfortunately, they are occurring with increasing frequency. Hundreds of homeowners in Massachusetts experience such leaks every year. While some occur in conjunction with a fire, most are the result of mechanical failure or human error. Mechanical failures include tanks rusting, copper feed lines corroding and steel tank legs rusting, which can cause a tank to tip over and spill. Human error often leads to more substantial releases. Items stored on or near tanks may be knocked over, breaking the fuel line and allowing the tank contents to drain out. Similarly, homeowners or utility workers can trip over and damage feed lines or use tank filters as stepladders. Inexperienced oil delivery personnel can over-pressurize a tank and cause it to fail. The worst oil spills often occur after converting from oil heat to gas. If the fill pipe at the exterior of the house is not removed, the oil company may attempt to fill a non-existent tank and fill the basement instead. When a spill occurs, the cleanup plan depends on the type of spill. Under a best-case scenario—a small spill in which oil is contained within a basement with concrete floors and walls—cleanup involves absorbing the oil, removing and disposing of all oil-impacted materials, and washing to remove oil odors. In the worst case—a spill of 275 or more gallons of oil in which the oil travels through a concrete or dirt floor and impacts soil or groundwater—cleanup may involve shoring, moving or even replacing the house, excavating soil or treating groundwater. Cleanup costs can range from several thousand to more than one hundred thousand dollars. At the Silvas' house, I worked with other environmental engineers and cleanup specialists to assess and cleanup the oil release. First, we collected and analyzed soil and groundwater samples from beneath the house to establish the nature and extent of the oil release. Fortunately, sampling of the Silvas' well indicated that the oil had not impacted their water supply. However, soil was contaminated to a depth of ten feet below the foundation. Guided by the Massachusetts Department of Environmental Protection's standards for oil release cleanup, we determined that up to 125 tons of oil-contaminated soil would need to be removed. (It could have been much worse. A full 275-gallon oil tank could theoretically contaminate 11.5 million pounds of soil—about 250 dump truck loads.) After the demolition of the Silvas' house and the removal of the foundation, cleanup personnel began excavating the contaminated soil. Under the watchful eye of Dick Silva, who was anxious to get on with construction, the soil was excavated and transported to an asphalt batch plant to be recycled as matrix material for asphalt. When soil sampling confirmed that cleanup standards had been met, the excavations were backfilled and the Silva brothers quickly compacted the clean fill to begin construction of the new house's footings.