Case Study: Large Scale Cleanup of NAPL in Riverbed — River Diversion and Restoration, Fort Collins, Colorado, USA

摘要

A manufactured gas plant (MGP) operated in Fort Collins, Colorado during the early 1900s. Downgradient of the MGP, a landfill operated until the late 1960s where a community center, athletic fields, and daycare center currently reside. The Cache La Poudre River lies adjacent to and downgradient of the former landfill. In 2002, when the river was at a historic low, tar-like non-aqueous phase liquid (NAPL) appeared in riverbed sediments. Characterization of impacts and sources revealed NAPL in bedrock fractures and alluvial sediment beneath the river and adjacent areas. River flow fluctuations influence appearance of NAPL and vertical flow mechanics in and around the river. Remedy selection, design, and implementation were accelerated to accommodate these fluctuations. The remedy included river diversion, removal/disposal of NAPL-impacted sediment/bedrock, installation of a subsurface vertical barrier with hydraulic controls, and comprehensive site restoration. The project was completed on schedule with acceptance by stakeholders and the community.