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02.15.2007 - GeoEngineers GEOENGINEERs February 15, 2007 Oregon Department of Environmental Quality 2020 SW Fourth Avenue, Suite 400 Portland, Oregon 97204-1912 Attention: Loren Garner Subject: DRAFT Planned Construction Activities Tigard Library,Tigard,Oregon File No. 4025-003-02 INTRODUCTION GeoEngineers has prepared this draft letter on behalf of the City of Tigard(City)to present information to the Oregon Department of Environmental Quality (DEQ) regarding planned construction activities at the Tigard Library property, located at 13125 SW Hall Boulevard in Tigard, Oregon (site). Several phases of environmental investigation and remediation related to arsenic in soil have been conducted at the site. The DEQ Environmental Cleanup Site Information(ECSI)number for the site is 4063. The City is preparing to extend the Wall Street right-of-way (ROW) across the southern portion of the site, approximately to the bank of Fanno Creek. The City is also planning to conduct landscaping activities in a planted area within the main library parking lot. The location of the planned ROW and parking lot are shown on Figure 1. The proposed ROW crosses soil that contains concentrations of arsenic that exceed DEQ default background concentrations for soil (DEQ, 2002), as well as generic screening criteria for humans and ecological receptors. The proposed landscaping activities will occur in soil that contains concentrations of arsenic that exceed generic screening criteria for humans. The concentrations of arsenic in soil at the site do not exceed the DEQ pre-calculated hot spot level for industrial land use (DEQ, 2005) although some areas exceed the residential hot spot concentration. A summary of arsenic concentrations in soil was presented in Hahn and Associates' "Draft Supplemental Site Investigation Report, Tigard Library", dated October 6, 2006. The proposed roadway and landscaping activities will result in the placement of caps over some of the most contaminated soil at the site and will reduce the potential for human and ecological exposure to arsenic and reduce overall site risk. As a result, the roadway and landscaping activities are partial remedies for contamination and will be considered during GeoEngineers' ongoing human health and ecological risk assessments at the site. DETAILS OF PLANNED ROADWAY CONSTRUCTION Construction of the Wall Street extension is planned for July 2007. Contractor bid packages will be provided to prospective bidders in late February 2007. The area to be covered by the roadway is shown on Figure 1. Construction plans call for 0 to 5 feet of fill, with fill thickness generally increasing toward EaXtB`Scvenep+.t6cfinplogy, 3 16458 SSS nquo�a Pkwy xei Mace 5119". 7a Stott§���Q fa*M 03 z � w1vv,,�eue�rg�pebts.00rn ,: C�oCtl DRAFT Oregon Department of Environmental Quality February 15,2007 Page 2 the east. Cuts are not planned; however, organic surficial material will be stripped prior to construction. Also,in some areas,limited trenching may be conducted for installing subsurface utilities. After the surface is stripped, a geotextile will be placed on the native soil and imported fill and asphalt pavement will be placed over the geotextile. The Wall Street extension will serve as a permanent cap over contaminated soil. The geotextile will serve as a demarcation layer to mark the boundary between clean fill and contaminated soil during future excavation activities. SOIL AND DUST MANAGEMENT Limited amounts of soil will be excavated during roadway construction. The excavated soil may be arsenic-contaminated based on previously collected data. The City will direct the construction contractor to take the following steps to minimize the potential for exposure to arsenic in soil: • Excavated soil will either be direct-loaded into trucks for transport to an appropriate disposal facility or will be stockpiled on an impermeable surface, such as plastic, concrete, or asphalt, prior to off-site disposal. • Stockpiled soil will be covered daily and bermed to prevent runoff. • Trucks carrying contaminated soil will be covered during transport to the landfill. • The contractor will take appropriate steps to minimize the mobilization of contaminated soil during construction activities. • The contractor will take appropriate measures to maintain a condition of no visible dust during construction(i.e. watering or application of other dust reducing compounds). • The contractor will take appropriate steps to ensure that excavated soil does not spill into Fanno Creek. • Contaminated soil will be disposed of at a licensed Subtitle D landfill, such as Waste Management's Hillsboro Landfill. DETAILS OF PLANNED LANDSCAPING The City plans to re-plant a landscaped area in the center of the existing library parking lot (parking lot island). Arsenic has been detected in soil at the west half the parking lot island at concentrations as high as 25 milligrams per kilogram (mg/kg), which exceeds generic human health risk screening criteria, but does not exceed likely ecological risk screening criteria. Arsenic has not been detected at the east half of the parking lot island at concentrations exceeding generic human and ecological risk screening criteria. The planned landscaping activities include removal of existing grasses and selected other plants, laying weed block fabric, re-planting native plants, and applying an approximately 4-inch-thick layer of bark dust. Soil will not be removed from the parking lot island. The proposed landscaping activities will lead to conditions that are protective of human health, without damaging mature native trees that are present in the parking lot island. The bark dust will provide a cover preventing direct contact with contaminated soil. The bark dust will also prevent contact with soil dust, File No.4025-003-02 GwENGINEER:� DRAFT Oregon Department of Environmental Quality February 15,2007 Page 3 reducing the risk of exposure through inhalation and ingestion. The weed block fabric will further reduce the potential for contact with native soil and will serve as a demarcation layer that will be useful for maintaining an appropriate thickness of bark dust. The bark dust and weed block will function as a cap over soil contamination and will be considered a partial remedy during the ongoing human health and ecological risk assessments at the site. CONCLUSIONS The City would like to proceed with landscaping activities in the parking lot island in March 2007. Construction of the new Wall Street ROW will occur in July 2007. The proposed site improvements will reduce the potential for human and ecological exposure to arsenic in soil and will reduce potential risks to human and ecological health. The roadway fill and asphalt and the bark dust will be considered engineered caps for the ongoing human health and ecological risk assessments. On behalf of the City, we request that DEQ issue an opinion regarding the proposed construction and landscaping activities. REFERENCES Hahn and Associates, Inc. October 6, 2007. Draft Supplemental Site Investigation Report, Tigard Library. Oregon Department of Environmental Quality, October 28, 2002. Default Background Concentrations for Metals, presented by the Toxicology Workgroup in a memorandum to DEQ Cleanup Project Managers. Oregon Department of Environmental Quality May 31, 2005. Final Pre-Calcluated Hot Spot Look-Up Tables. File No.4025-003-02 GEdENGINEER DRAFT Oregon Department of Environmental Quality February 15,2007 Page 4 If you have any questions or comments regarding the planned activities,please contact the undersigned at 503-624-9274. Sincerely, GeoEngineers,Inc. Chris W. Breemer,R.G. Senior Project Manager John H. Biggane Principal CWB:JHB:glb PORT:\4\4025003\02\Finals\402500302L.doc Attachment: Figure 1.—Site Layout c: Dennis Koellermeier,City of Tigard Disclaimer: Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record. Copyright©2007 by GeoEngineers,Inc. All rights reserved. File No.4025-003-02 GEoENGINEER