Remedial Action Report Construction Phase

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5.1 Former Senator Parking Lot (Areas 3 and 24 and UST-14) Area 3 During pre-construction, three USTs, labeled UST-1, UST-2, and UST-3, were discovered beneath the High Street sidewalk near the intersection with Chemeketa Street (Figure 4). The USTs were most likely associated with the former Harbison gasoline station. UST-1, UST-2, and UST-3 had volumes of 4,000, 2,000, and 2,000 gallons, respectively. The three USTs were decommissioned in place during pre-construction to preserve the structural integrity of the paving on High Street and potential underground utilities. Soil samples were collected beneath the USTs during pre- construction and analyzed for total petroleum hydrocarbons. Analytical results indicated concentrations of diesel and kerosene below the 500 mg/kg soil matrix cleanup level (Century West 1998b). During the construction phase, UST-1, UST-2, and UST-3 required removal based on a modification in the building design. After the USTs were removed, Century West visually assessed the soil beneath the USTs and used a PID to screen for potential volatiles. No evidence of petroleum contamination was observed. Groundwater was not observed in the excavations. A copy of the CJ Environmental decommissioning report far the three USTs is provided in Appendix E. During pre-construction remedial actions, approximatel}~ 500 tons of petroleum hydrocarbon impacted soil was removed from Area 3. The depth of the remedial excavation was approximately 10 feet below street grade. During the construction phase, an additional eight tons of contaminated soil was excavated from this area due to the unsuitable geotechnical properties of the soil. The soil removed from two small pockets of petroleum h}~drocarbon impacted soil which were approximately ten feet in diameter and one foot thick were disposed off-site. Groundwater was not observed in the excavations. Confirmation soil sample 3-3-14.5 was collected from the northern excavation and analyzed for NWTPH-HCID with quantification and BTEX. Confirmation sample 3-4-14.5 was collected from the southern excavation and analyzed for NWTPH-Gx and BTEX. Figure 5 shows the location of the samples and the e~tent of contaminated soil removed from Area 3 during the construction phase. Mineral spirits were detected in soil samples 3-3-1~.~ and 3-4-14.5 at concentrations of 405 mg/kg and 283 mg/kg, respectively (Table 2). The concentrations of mineral spirits (gasoline range) detected in these soil samples exceed the 80 mg/kg soil matrix cleanup level. However, concentrations of toluene, ethylbenzene, and xylenes detected in these samples were significantly below the applicable RBCA Tier I RBSLs (Table 2). Construction Phase - Remedial Actions - 10 - 4080600127 Courthouse Square November 9, 1999