Remediation of a 115,000-gallon petroleum pipeline leak

A rupture in a buried petroleum pipeline in June, 1988 released 115,000 gallons of diesel fuel, contaminating soil and ground water at a site in Milwaukee, Wisconsin. Emergency and interim response actions resulted in the recovery of over 70,000 gallons of product from the ground surface, a nearby creek, and recovery trenches. Based on the results of a contamination assessment, the most cost effective and technically feasible remedial alternative included low temperature thermal desorption for treatment of the impacted soils, and recovery of impacted ground water with discharge to a sanitary sewer. The implementation of the thermal desorption process was the first application of its type in the State of Wisconsin. Approximately 10,000 cubic yards of soil, with a total petroleum hydrocarbon (TPH) concentration of up to 24,000 parts per million (ppm), was treated at the site using the thermal desorption system. Using a feed rate of approximately 20 tons per hour, the impacted unconsolidated materials, varying in composition from gravelly sand to silty clay, were heated to 400 to 500 degrees F in a propane-fired rotary kiln. In the process, petroleum was vaporized off the soils and then completely oxidized at 1450 degrees F in an afterburner. After processing, the soil was replaced in the excavation with a TPH concentration of less than 10 ppm. Impacted ground water is still being treated at the site using a 225-foot long interception trench. An automated pumping system recovers slightly impacted ground water which is subsequently discharged to the sanitary sewer. Residual free product is collected from the water surface manually using oil skimming devices. Dissolved volatile organic compounds (VOCs) total less than 5 ppm; therefore no treatment is required prior to discharge to the sewer. Pending approval of a permit application, discharge will be to a nearby stream