A containment system was designed under a Consent Order with the WDEQ to prevent off-site migration of contaminated groundwater and LNAPL. An alternative evaluation design was used to select a soil bentonite slurry wall with a series of interceptor. Data from a detailed subsurface investigation was used to design a 1,700-foot long by 25-foot deep slurry wall with 500 feet of interceptor trenches using biodegradable polymer construction techniques with consideration for pipelines and other utilities at an active refinery. The work included preparation of construction plans, construction oversight, performance evaluation, and long-term performance monitoring. A groundwater treatment system was designed and an NPDES permit application was submitted and approved for treated water discharge to a creek. The treatment system consisted of an oil/water separator and an air stripper with pretreatment to reduce maintenance due to fouling.