Remedial Action Report Construction Phase

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EXECUTIVE SUMMARY Century West Engineering Corporation (Century West) was retained by Marion County to conduct site investigation and remedial actions for the Courthouse Square project located in downtown Salem, Oregon (Figure 1). The project involves redevelopment of an entire city block. In the summer of 1997, surface structures on the Courthouse Square property were demolished, including buildings, parking structures, and paved areas. Currently, a subterranean parking structure is being constructed to a depth of approximately ten feet below street grade extending throughout the block. Above ground, the southern portion of the site will be developed for office/retail use. The central portion of the site will be developed as a transit mall. The northern portion will be left for future development and may include residential units. This document summarizes remedial actions conducted during the initial phase of construction between March 15, 1999 and August 5, 1999. The purpose of the construction phase remedial actions was to manage environmental issues on the Courthouse Square property in accordance with state and local regulations and secure a"no further action" determination for the property from the Oregon Department of Environmental Quality (DEQ). Specific objectives of the construction phase remedial actions included: 1) ensuring worker safety related to subsurface contamination, 2) characterizing the nature and extent of subsurface contamination, 3) managing water generated during construction dewatering operations, 4) managing the excavation, transport, and disposal of contaminated soil, and 5) evaluating the risk associated with potentially contaminated soil and/or groundwater left in place. Based on the findings from the construction phase remedial actions at the Courthouse Square property, the following conclusions are presented: The identified contaminants of concern are petroleum hydrocarbons. Approximately 2,640 tons of petroleum hydrocarbon impacted soil was removed from the Courthouse Square property during the construction phase and transported to the Riverbend landfill in McMinnville, Oregon for disposal. 2. Approximately 385 cubic yards of petroleum hydrocarbon impacted soil containing concentrations exceeding the DEQ soil matri~ cleanup levels was left in place. The extent of the impacted soil has been delineated and, based on the results from constituent analysis, does not pose a risk to human health or the environment. During dewatering operations, approximately 1,413,645 gallons of water was discharged into the storm drain in accordance with state and local requirements. 4. Based on analytical results, groundwater at the site does not contain contaminants at concentrations exceeding the DEQ cleanup levels. -ii-