Gasco Profile


Gasco is a former manufactured gas plant which deposited wastes into upland tar ponds for many years. The site is located near river mile 6.5 between the St. Johns and Railroad bridges on the southwest side of the Willamette River. The tar ponds overflowed into the Willamette River for decades. The overflow remnants were visible during low river stages and were eroding. Removal of tar deposits in the river was completed in the fall of 2005. These deposits contained hazardous substances such as TPAH, benzene, and cyanide (For a full list of pollutants found in the Portland Harbor, click here)

History of the Site and Contamination

According to the EPA:

Gasco purchased the site in approximately 1910.  At that time, the site was larger, approximately 85 acres.  Today the site is 44.65 acres.  Gasco built and operated an oil gasification plant on the site between 1913 and 1956.  Between 1913 and 1923, only gas and lampblack briquettes were produced.  In 1923, by-products refining began.  After 1925, when tar refining operations began, the quantity of tar within the waste stream would have decreased, but waste tar in the effluent continued to occur as suspended material and emulsions from the secondary tar box.  Prior to 1941, all wastewater effluent and tar stills from the gasification process and by- product refining was discharged to a stream channel leading from the production area to the Willamette River, or to low lying areas of the site.  After 1941, wastewater effluent and tar stills were disposed of into settling ponds adjacent to the Willamette River in the central portion of the Gasco facility including what is now part of the Siltronic property.  Historic photographs suggest that the tar ponds periodically overflowed to the Willamette River.  When the plant was shut down in 1956, an estimated 30,000 cubic yards of tar waste had accumulated in the ponds.  The southern portion of the original Gasco property was sold and is now owned by Siltronic Corporation (Siltronic).  The tar ponds on the northern portion of the site were buried under 10 feet of fill in 1973. Current uses of the Gasco site, other than as a liquefied natural gas plant, are bulk transfer of creosote oil and coal tar pitch, liquefied gas storage, and bulk petroleum storage.  (Gasco Siltronic Approval Memo, p. 1-2)

Operation of the property by Siltronic resulted in additional releases of Trichloro-ethylene (TCE).

Early Action

As mentioned above, early action in 2005 removed tar deposits that contained hazardous substances such as TPAH, benzene, and cyanide

In 2009 EPA found that "[c]ontaminants known to be present at the Gasco/Siltronic facility that pose a substantial risk to human health or the environment include naphthalene, cyanide, benzene, tars, oil, creosote, phenols, polynuclear aromatic hydrocarbons (PAHs), BTEX, phthalates, Carbazole, chlorophenol, chrysene, cobalt, DDT, dibenzofuran, dimethylphenol, ethylbenzene, pyrenes, manganese, PCP, VOCs, (such as vinyl chloride, TCE, toluene, and others which are commingled with MGP wastes) and lead, starting in the uplands and continuing through the riverbank and into sediment in the river."  (Gasco Siltronic Approval Memo, p. 4-5).

EPA found the site to have the highest levels of PAHs in the harbor.

EPA approved development of an EE/CA to analyze early action cleanup in light of the greater harborwide RI/FS and ROD processes.


Stay tuned for updates on any cleanup activity at this site.


Other Upland Sites Administed by DEQ:




Doane Lake (Rhone-Poulenc)




Kinder Morgan Liquid Terminals (Linnton)

Mar-Com South Parcel

Oregon Steel Mills- Rivergate

Premier Edible Oils

Schnitzer Burgard Industrial Park

Schnitzer Steel

Wacker Siltronic, Corp. (NW Natural Gas)

Willbridge Terminal (Multiple PRPs)