Site Investigation Report Addendum Nehalem Highway 101 Right-of-Way Nehalem, Oregon Prepared for: Oregon Department of Environmental Quality Task Order 57-08-20 October 14, 2010 1674-00/Task 5 Table of Contents 1.0 INTRODUCTION ..................................................................................................................................... 1 1.1 Purpose ............................................................................................................................................... 1 1.2 Scope of Work..................................................................................................................................... 1 2.0 BACKGROUND ....................................................................................................................................... 2 2.1 Site Location and Description.............................................................................................................. 2 2.2 Current and Past Site Use................................................................................................................... 2 2.3 UST Discovery, Removal, and Sampling............................................................................................. 3 2.4 Impacted Areas in Site Vicinity ............................................................................................................ 3 2.5 2009 Site Investigation Results and Conclusions................................................................................ 4 3.0 METHODS AND PROCEDURES ............................................................................................................ 5 3.1 Groundwater Monitoring ...................................................................................................................... 5 3.2 Handling of Investigation-Derived Waste............................................................................................. 6 4.0 CHEMICAL ANALYSES AND RESULTS ................................................................................................ 6 4.1 Analyses Performed ............................................................................................................................ 6 4.2 Chemical Results................................................................................................................................. 6 5.0 ANALYTICAL DATA AND RISK-BASED SCREENING........................................................................... 7 6.0 CONCLUSIONS....................................................................................................................................... 8 7.0 REFERENCES ........................................................................................................................................ 9 Tables 1 Monitoring Well Construction and Groundwater Elevation 2 Groundwater Analytical Results: Petroleum Hydrocarbons, PAHs, and Lead 3 Groundwater Analytical Results: VOCs Figures 1 Site Location Map 2 Site Plan 3 Groundwater Elevations (9/16/2010) 4 TPH Concentrations in Groundwater Appendix A Laboratory Analytical Report and Data Quality Review Site Investigation Report Addendum Page i Nehalem Highway 101 ROW, DEQ Task Order No. 57-08-20 October 14, 2010 1674-00/Task 5 1.0 Introduction This Site Investigation (SI) Report Addendum describes the results of groundwater monitoring activities at and in the vicinity of the northeast corner of the intersection of H Street and 7th Street in Nehalem, Oregon (the Site). The project Site is the area immediately surrounding the former location of underground storage tanks (USTs) adjacent to the former location of a service station at 36005 7th Street in Nehalem, Oregon (Figure 1). The groundwater monitoring event was conducted on September 16, 2010 for the Oregon Department of Environmental Quality (DEQ) under a Leaking Underground Storage Tank (LUST) Corrective Action Cooperative Agreement using funding provided by the American Recovery and Reinvestment Act of 2009 (ARRA). This report was prepared for the DEQ under Task 5 of Task Order No. 57-08-20. 1.1 Purpose In 2006, the Oregon Department of Transportation (ODOT) discovered three USTs in the right-of-way during a highway reconstruction project. It is believed that the three USTs were a remnant of the historical operations of a gas station.. Limited sampling was conducted by ODOT as part of the tank decommissioning, but the extent of impacts from historical releases from the tanks was unknown. A November 2009 SI was conducted to define the magnitude and extent of impacts related to the former gasoline tanks at the Site. The results of the SI were documented in the Site Investigation Report (Ash Creek Associates [Ash Creek], 2010). The results of the SI showed concentrations of two polycyclic aromatic hydrocarbons (PAHs) detected in the sample from well MW-3 (located 60 feet from the Nehalem River) slightly exceeding relevant screening levels. The SI sampling event was conducted immediately after the Site area flooded due to the high Nehalem River Level. This groundwater monitoring event was conducted to assess the concentrations of site constituents in the installed groundwater monitoring wells during the dry season and a low river stage. 1.2 Scope of Work The scope of work was completed in general accordance with the Site Investigation Work Plan (Work Plan) dated October 16, 2009 (Ash Creek, 2009). Activities consisted of the following tasks: Measurement of depth to water in the three installed groundwater monitoring wells; Collection of groundwater samples from the groundwater monitoring wells and analysis of groundwater samples for volatile organic compounds (VOCs); PAHs; lead; and total petroleum hydrocarbons as gasoline (TPHg), diesel (TPHd), and oil (TPHo); and Preparation of an SI Report Addendum that summarizes groundwater monitoring activities and analytical results, and evaluates potential risk based on the SI and groundwater monitoring results. These activities are discussed in detail within this report. Site Investigation Report Addendum Page 1 Nehalem Highway 101 ROW, DEQ Task Order No. 57-08-20 October 14, 2010 1674-00/Task 5 2.0 Background This section presents a description of the Site, the geology and hydrogeology, and summarizes the results of previous soil and groundwater sampling that has been completed. Tables and figures compiling the historical activities and analytical results were presented in the Work Plan (Ash Creek, 2009). 2.1 Site Location and Description The Site consists of the right-of-way (ROW) at the northeast corner of 7th Street and Highway 101 – also known as H Street – in the City of Nehalem, Oregon (Figure 1). The Site is located in the SW 1/4 of the NE 1/4 of Section 27, Township 3 North, Range 10 West, Willamette Meridian. The Site has been defined as the location of three abandoned USTs found by ODOT during a 2006 highway reconstruction project, and the area immediately surrounding the tanks (Figure 2). As described below in Section 2.3, the USTs were removed in 2006 by ODOT, who reported petroleum contamination in the soils and groundwater surrounding the tanks. The Site is currently covered by a sidewalk. The ROWs that make up the Site at the junction of H and 7th Streets are owned by the City of Nehalem and Tillamook County, respectively. ODOT maintains an easement over the property and is not a property owner. The USTs at the Site were associated with the former service station located at 36005 7th Street in Nehalem, Oregon, directly to the east of the Site. The former service station property associated with the Site is currently operating as a retail establishment (Hal’s Annex). Properties surrounding the Site are predominantly commercial but include some residential. The Site is bounded to the west by 7th Street, to the east by Hal’s Annex, to the north by a retail establishment, and to the south by H Street. Figure 2 shows the Site layout and surrounding properties. The Site is approximately 0.01 acre in size. The study area of this SI also includes portions of the former service station property associated with the Site, H Street, 6th Street, 7th Street, and the ROW of Highway 101. The ground surface across the study area is relatively flat, with the ground surface sloping slightly toward the Nehalem River (east). The majority of the study area is paved or covered by buildings or sidewalks. 2.2 Current and Past Site Use Historical Site Use. A Phase I Environmental Site Assessment (ESA) for a nearby property included historical information about the Site (Grant Associates, 2007). Sanborn Fire Insurance maps were reviewed and indicate that the adjacent Hal’s Annex property was an operating service station prior to 1921 (copies from the referenced report were included in Appendix B of the Work Plan). In a letter to the DEQ, Nehalem City Manager Michael Nietzsche indicated that the service station ceased operations between 1976 and 1978. Mr. Nietzsche also indicated, and provided photographs showing, that formerly the facility operated as a mill, which made barrel staves and wooden boxes in 1914. Sanborn Fire Insurance maps show that a Site Investigation Report Addendum Page 2 Nehalem Highway 101 ROW, DEQ Task Order No. 57-08-20 October 14, 2010 1674-00/Task 5 small structure with one UST was built before 1921 and that a garage/service station similar in size to the current structure at Hal’s Annex was built between 1921 and 1931. In the late 1930s, ODOT obtained highway right-of-way for the site with