Wilder Projects

Tacoma Historical Coal Gasification Site

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Project Location: Tacoma, Washington

Client: Washington Natural Gas

Construction Cost: $30 million

Wilder’s Role: Prime

Construction Period: 5/92 - 9/95

Project Highlights

  Solidification of Contaminated Soils and auto fluff debris
  Heavy Metals, Coal Tar and Auto Fluff Contamination
  Drainage of two contaminated ponds
  Pump and Treat Contaminated Groundwater
  Dredged Material Dewatering
  On-Site Disposal with HDPE Cover
  Installation of Leachate Drains
  Concurrent Site with Operations Active Metal Recycler
  Off-Site disposal of contaminated soil
  NPL Site returned to productive use

The Tacoma Historical Coal Gasification Site occupied fifty acres and included an active metal recycling facility. Contaminants included heavy metals, PAHs, TPHs, PCBs, and BTEXs in media of soil, rubble, debris, auto fluff, coal tar and water. Activities on site were overseen by the EPS, EPA’s oversight contractor (CH2M Hill), local agencies (WA DOE), the design engineer’s site coordinator (Ebasco), and the owner’s project manager (Washington Natural Gas). Wilder performed all on-site remediation work categorized in two phases.

Phase I (May 1992 through July 1993)

The first phase of remediation work involved excavation of contaminated soil, tar (extremely hazardous waste designation by Washington State), and auto fluff (a lightweight, non-metallic material produced from shredding car interiors) which were excavated and stockpiled separately. Sheetpiling (1,900 LF) driven 34 feet into the ground separated two water filled ponds of tar contaminated soil from an auto fluff area. These sheetpile cells ultimately became containment for stabilized material (Phase II). Total excavation quantities for Phase I included 23,000 CY of metals contaminated soil; 24,000 CY of auto fluff and 28,999 CY of tar. Over 100,000 TN of import fill were brought on site for backfill material. Following excavation, clamshell dredging and dewatering, contaminated material was stabilized using Wilder’s pugmill plant. A total of 47,000 CY of material were stabilized. The stabilized end product was placed in containment cells constructed on site, roller-compacted and covered.