Geotechnical exploration during design of the $100 million Tacoma Spur Freeway (SR 705) revealed unexpected coal tar contamination. This discovery was traced to a long-abandoned coal gasification plant which operated on the site around the turn of the century. Further discoveries during construction included two large, buried tanks filled with tar waste, and copper contamination from ore spilled in an old train derailment. A three-year co-operative effort by the Washington State Department of Transportation (WSDOT) and the Washington State Department of Ecology (WSDOE), assisted by a hazardous waste consultant, ensured that design and construction proceeded with minimal delay. Solutions produced by the joint effort included three specially designed on-site concrete vaults for storing 26,450 tons of problem waste and the removal of 15,900 tons of extremely hazardous waste to a hazardous waste facility in Arlington, Oregon. In addition, 1300 tons of copper-contaminated soil were removed and transported to a smelter in El Paso, Texas, for recovery of the ore. Total project cleanup costs were almost $6 million. Long-term groundwater monitoring has been planned and is expected to show a significant decrease in previous contaminant concentrations reaching the adjacent City Waterway.
Abstract