Department of Environmental Quality

DEQ Home/ Land Quality/ Environmental Cleanup/ ECSI/ Site Summary Full Report

Environmental Cleanup Site Information (ECSI) Database Site Summary Full Report - Details for Site ID 84, GASCO

This report shows data entered as of October 23, 2021 at 10:22:16 PM

This report contains site details, organized into the following sections: 1) Site Photos (appears only if the site has photos); 2) General Site Information; 3) Site Characteristics; 4) Substance Contamination Information; 5) Investigative, Remedial and Administrative Actions; and 6) Site Environmental Controls (i.e., institutional or engineering controls; appears only if DEQ has applied one or more such controls to the site). A key to certain acronyms and terms used in the report appears at the bottom of the page.

Note: DEQ may have posted online documents related to this site. If so, they would be available for viewing or downloading on ECSI Summary Page

Go to DEQ's Facility Profiler to see a site map as well is information on what other DEQ programs may be active at this site.

General Site Information

Site ID: 84 Site Name: GASCO CERCLIS No: 027734359
Address: 7900 NW St. Helens Rd. Portland 97210
  County: Multnomah Region: Northwest
Other location information: See GDSC for location information.
Investigation Status: Listed on CRL or Inventory
  Brownfield Site: No NPL Site: No Orphan Site: No Study Area: No
Property: Twnshp/Range/Sect: 1N , 1W , 12 Tax Lots: 42,111,123,113,129,131,112,130
  Latitude: 45.5788 deg. Longitude: -122.7583 deg.  Site Size: 35 acres
Other Site Names:
  Koppers Co. - Portland
  NW Natural Gas Company
  Pacific Northern Oil Co.
  Portland Harbor Sediment Study
  Fuel and Marine Marketing
  Pacific Terminal Services
  Northwest Natural
  NW Natural
  Gasco Facility
  Former Gasco Manufactured Gas Plant Operable Unit

Site Characteristics

General Site Description: The Gasco Site is located on property owned by NW Natural at 7900 NW St. Helens Road in Portland, Oregon (NW Natural Property) on the westside of the Willamette River between river mile 6 and 6.5. The site occupies approximately 40-acres and is zoned industrial. NW Natural uses the site for the storage and distribution of liquefied natural gas (LNG). A portion of the site is leased for marine fuel storage and distribution.

Contaminant investigation and risk assessment in the uplands of the site is nearing completion, and cleanup options for soil and groundwater are currently being evaluated under DEQ. Separately, cleanup design work for the site riverbank and in-water contamination are being completed under EPA as part of Portland Harbor Superfund Site work.
Site History: From 1913 until 1956, NW Natural, then known as the Portland Gas & Coke Company (GASCO) owned and operated a manufactured gas plant (MGP) and by-products processing facility (GASCO MGP) on the NW Natural Property. The former GASCO property included approximately 40-acres of the adjoining property known as the Allen Tract that now comprises the northern portion of an 85-acre property currently owned by Siltronic Corporation (Siltronic) at 7200 NW Front Avenue in Portland, Oregon (Siltronic Property). GASCO MGP operations ceased in 1956. GASCO sold the Allen Tract to private co-purchasers in 1962.

Leaseholds on the NW Natural Property have historically been used by companies involved in coal tar, creosote, and pitch operations (i.e., Beazer East, Inc. [formerly Koppers Company, Inc.]) and Koppers, Inc. [formerly Koppers Industries, Inc.]), and for storage and distribution of marine fuel (i.e., Fuel and Marine Marketing and Pacific Terminals). Coal tar, creosote, and pitch operations occurred in the southern portion of the NW Natural Property from 1966 to the fall of 2018. Marine fuel storage has occurred on a leasehold located in the central portion of the property adjacent to the river since 1965. Currently the NW Natural Property is utilized by NW Natural for an LNG operation, and by Pacific Terminals as a marine fuel storage and distribution terminal.

In 1978, Siltronic purchased approximately 85-acres adjacent to and southeast of the NW Natural Property, including the former Allen Tract (now the 40-acre northern portion of the Siltronic Property), for the purpose of constructing and operating a silicon wafer fabrication plant. Silicon-wafer manufacturing began on the Siltronic Property in 1980 and is ongoing.
Contamination Information: GASCO built a gas manufacturing plant on the NW Natural Property in 1912 and 1913, relocating manufacturing operations downriver from downtown Portland (Portland Gas Mfg., ECSI#1138). Historic GASCO MGP production generated large quantities of manufacturing byproducts, or residuals; that were used as, or incorporated into fill across the historic operations area, and discharged into unlined ponds and the Willamette River. Byproducts of the GASCO MGP operation included lampblack briquettes, light oils, tars, and electrode grade coke. Wastes generated at the GASCO MGP included tar, lampblack, wastewater containing dissolved and suspended hydrocarbons, and spent oxide. The MGP wastes were disposed of on the NW Natural Property and the northern portion of the Siltronic Property in piles and tar ponds. Subsequent to the end of GASCO MGP operations, releases from coal tar, creosoting, and pitch company operations into soil and groundwater occurred in southern portion of the NW Natural Property. Wafer manufacturing in the northern portion of the Siltronic Property (ECSI #183) involved the use of solvents. Solvent releases to soil and groundwater occurred from a former underground tank system adjacent to the southwest side of the Fab 1 Building and from an unknown source located at the Central Facilities Building.
Manner and Time of Release: Management of MGP residuals occurred on the NW Natural Property throughout the life of the GASCO MGP between 1913 and 1956. The MGP residuals were placed in piles and discharged to ponds (effluent discharge, settling, storage, and overflow ponds) located in non-production areas. From 1913 to 1941 wastewater containing dissolved and suspended hydrocarbons were discharged to low lying areas of the site with drainage features leading from the GASCO MGP production areas to the Willamette River. Effluent ponds expanded over time onto the adjoining Allen Tract. The MGP residuals were piled and discharged into effluent ponds between 1941 and 1956. Reportedly, between 1965 and 2018 spills, land application, and burial of contaminated material from former coal tar, creosote, and pitch operations periodically occurred during the time period companies occupied the southern leasehold. Following its sale by GASCO in 1962, MGP wastes within the Allen Tract were redistributed and incorporated into fill across portions of the current Siltronic Property between 1966 and 1975.

Releases associated with historic solvent use by Siltronic in the northern portion of the Siltronic property occurred between 1980 and 1984 from a former solvent underground storage tank system and an unknown source.
Hazardous Substances/Waste Types: The primary MGP residual types found at the site in fill and shallow groundwater within the fill include, lampblack, purifier box wastes (spent lime and spent oxides); tar, and oil. The oil is a dense non-aqueous phase liquid (DNAPL) that occurs in the fill, and beneath the fill in the areas of the former tar ponds. The MGP residuals are sources of contamination for metals (examples - arsenic, lead, zinc), total petroleum hydrocarbons, polycyclic aromatic hydrocarbons ([PAHs] examples - benzo[a]pyrene, benzo[a]anthracene, naphthalene), volatile organic compounds ([VOCs] examples - benzene, ethylbenzene), semi-volatile organic compounds (examples - carbazole, dibenzofuran); and other inorganic compounds (examples - cyanide and metal complexes, sulfide) in soil and/or groundwater.

Chemical constituents associated with releases from historic coal tar and creosoting operations include, PAHs (e.g., benzo[a]pyrene, naphthalene), VOCs (e.g., benzene, toluene, ethylbenzene, xylene), and total petroleum hydrocarbons.

Releases from Siltronic involve solvent DNAPL and chlorinated VOCs (cVOCs), particularly trichloroethene, and its associated degradation products, including cis-1,2-dichloroethene, trans-1,2-dichloroethene, 1,1-dichloroethene, and vinyl chloride. Solvent DNAPL occurs within a larger area of MGP DNAPL, residuals, and contamination from historic GASCO MGP operations in the northern portion of the Siltronic Property.
Pathways: Contamination in soil represents significant potential risk of exposure to human health (occupational, construction, excavation worker) and ecological receptors (plants, invertebrates, mammals, birds) in the uplands of the NW Natural Property and the northern portion of the Siltronic Property, including the riverbank. Shallow groundwater contamination in the fill is a complete contaminant transport pathway from the uplands to the Willamette River and a local surface drainage (Doane Creek) that represents significant potential risk of exposure to terrestrial ecological receptors exposed to riverbank seeps, and to ecological receptors in sediments and surface water. Deep groundwater contamination in alluvium below the fill is a complete contaminant transport pathway to the Willamette River that represents a significant potential risk of exposure to ecological receptors in sediments and surface water. Deep groundwater contamination also significantly and adversely affects the current beneficial uses of groundwater (Willamette River recharge) and the reasonably likely future use of groundwater under an industrial use scenario.
Environmental/Health Threats: See "Pathways" information.

Consistent with recommendations made by the Oregon Health Authority, DEQ requested that NW Natural post signs along the Gasco beach as a removal action. NW Natural posted the signage to prevent, minimize, or mitigate potential exposure to the public that might result from recreating on the beach, or generally coming into contact with sediment impacted by PAHs.
Status of Investigative or Remedial Action: DEQ determined in November 2015, that to expedite cleanup planning NW Natural will be responsible for completing a Remedial Investigation (RI), Human Health and Ecological Risk Assessment (HERA), and Feasibility Study (FS) of the former GASCO MGP operations area, including the NW Natural Property and the northern portion of the Siltronic Property. The historic GASCO MGP operations area represents the most contaminated portions of the two properties. DEQ identifies the historic operations area as the Former Gasco MGP Operable Unit (Gasco OU). NW Natural has completed RI and HERA reports for the NW Natural Property, a draft RI and HERA report for the northern portion of the Siltronic Property, and a draft interim FS document for the Gasco OU.

In the upland along ~2,200 feet of the Gasco OU shoreline, a well-based hydraulic control and containment (HC&C) system has been installed within the Alluvium water-bearing zones (WBZ) as a groundwater source-control measure (SCM). The HC&C system has been fully operational since December 2016 and controls migration of deeper contaminated groundwater to the Willamette River by pumping extraction wells to maintain groundwater levels in the Alluvium WBZ below the river (i.e., maintains the hydraulic gradient from the river towards the uplands). Groundwater pumped by the system is treated on-site before being discharged to the Willamette River. Free product recovery in upland site wells is also being performed. The HC&C system is being evaluated, along with other cleanup technologies, in the ongoing upland Gasco OU FS.

NW Natural has completed an evaluation of SCMs for shallow groundwater in the Fill WBZ. The evaluation identifies technologies to control shallow groundwater migration to the Willamette River along the Gasco OU shoreline. The Gasco OU FS will incorporate the evaluation into uplands remedy planning to facilitate integration of the uplands and in-water remedy designs.

Separately and under EPA oversight, NW Natural removed ~15,000 cubic yards of tar and heavily impacted sediments from the Willamette River in 2005. Removal addressed only a portion of tar present within the river.
Data Sources: 1. NW Natural Gasco Site - ECSI File #84
2. Siltronic Corporation - ECSI File #183
3. Doane Lake Study Area - ECSI File #36
4. DEQ Voluntary Agreement WMCVC-NWR-94-13 for RI/FS effective August 8, 1994, amended July 19, 2006 by Addendum 1 and Addendum 2 dated October 11, 2016
5. Hahn and Associates, Inc., 2007, Remedial Investigation Report, NW Natural - Gasco Facility, Portland, Oregon, April 30, a report prepared for NW Natural. DEQ comments letter dated March 10, 2010.
6. Anchor QEA, LLC, 2012, Revised Groundwater Source Control Construction Design Report, January 30, a report prepared for NW Natural. DEQ comments letter dated August 9, 2012.
7. Anchor QEA, LLC, 2014, Human Health and Ecological Risk Assessment Report - NW Natural Gasco Site. December (as revised by DEQ May 22, 2015 comments), a report prepared for NW Natural.
8. Anchor QEA, LLC, 2015, Fill WBZ Trench Design Evaluation Report - Gasco/Siltronic, April 8, a report prepared for NW Natural.
9. Anchor QEA, LLC, 2018, Draft Interim Feasibility Study, November 21 (revised by errata dated November 29, 2018 and January 11, 2019), a document prepared for NW Natural.
10. DEQ comments letter dated August 15, 2019.
11. Anchor QEA, LLC, 2019, Stormwater Source Control Measures and Performance Monitoring Annual Progress Report, a report prepared on behalf of NW Natural.

Substance Contamination Information

Substance Media Contaminated Concentration Level Date Recorded
BENZENE Groundwater 16 ppm  
BENZENE Sediment 22 ppm  
BENZENE Soil 360 ppm  
CYANIDE (AS ION) Groundwater 11 ppm  
CYANIDE (AS ION) Soil 50.7 ppm  
NAPHTHALENE Groundwater 30 ppm  
NAPHTHALENE Sediment 5,100 ppm  
NAPHTHALENE Soil 11,000 ppm  

Investigative, Remedial and Administrative Actions

Action Start Date Compl. Date Resp. Staff Lead Pgm
Site added to CERCLIS 07/01/1979  
EPA Basic Preliminary Assessment 12/23/1987 12/28/1987
Site added to database 05/03/1988   Michael Rosen SRS
Responsible party notified re 11/88 Inventory listing 11/30/1988   SAS
EPA Screening Site Inspection 1 12/15/1988 12/15/1988
SITE EVALUATION 03/16/1993 03/16/1993 Kevin Dana SAS
Listing Review completed 03/18/1993 03/18/1993 Kevin Dana SAS
Proposal for Confirmed Release List recommended 03/19/1993 03/19/1993 Kevin Dana SAS
Proposal for Inventory recommended 03/22/1993 03/22/1993 Kevin Dana SAS
Other remedial or investigative action recommended 03/23/1993 03/23/1993 Kevin Dana SAS
VCS Waiting List 08/13/1993 12/16/1993 Michael Rosen VCS
NEGOTIATIONS 12/16/1993 08/08/1994 Eric Blischke VCS
Facility proposed for Confirmed Release List 02/10/1994 02/10/1994 Eric Blischke VCS
Facility proposed for Inventory 02/10/1994 02/10/1994 Eric Blischke VCS
Owner/operator comments received on listing notification 02/22/1994 02/22/1994
REMEDIAL INVESTIGATION 03/21/1994 03/30/2010 Dana Bayuk VCS
Land-Use Assessment 03/21/1994 08/18/1997 Eric Blischke VCS
Review for final listing 04/04/1994 04/04/1994 Eric Blischke VCS
Listing on Confirmed Release List recommended 04/05/1994 04/05/1994 Eric Blischke VCS
Listing on Inventory recommended 04/05/1994 04/05/1994 Eric Blischke VCS
Facility placed on Confirmed Release List 04/06/1994 04/06/1994 Heather Schijf SAS
Facility placed on Inventory 04/06/1994 04/06/1994 Heather Schijf SAS
Letter Agreement 08/08/1994 08/08/1994 Dana Bayuk VCS
EPA Site Inspection Prioritization 02/15/1995 02/16/1995
No Further Remedial Action Planned under Federal program 02/16/1995 02/16/1995
Source Control Evaluation 08/02/2005   Dana Bayuk VCS
RISK ASSESSMENT 03/10/2010 05/22/2015 Dana Bayuk VCS
Beneficial Water Use Assessment 03/10/2010 01/05/2012 Dana Bayuk VCS
REMOVAL 08/01/2012   Dana Bayuk VCS
FEASIBILITY STUDY  (Primary Action) 07/27/2015   Dana Bayuk VCS

Key to Certain Acronyms and Terms in this Report:

You may be able to obtain more information about this site by contacting Dana Bayuk at the Northwest regional office or via email at If this does not work, you may contact Ximena Cruz Cuevas (503) 229-6811, or via email at or contact the Northwest regional office.