Project Description

In 2012, RGI was retained by Alamo Manhattan (Client) to perform standard due diligence services pertaining to the potential purchase of a property in downtown Bellevue, Washington. RGI conducted a Phase Environmental Site Assessment (ESA) on the property, which indicated that the property was formerly utilized as a dry cleaning facility and a gasoline service station.
Based on the findings of the Phase I ESA, RGI subsequently conducted subsurface investigations, which included advancing test probes on exterior and interior portions of the property (including inside the dry cleaning facility). RGI also conducted a geophysical survey and installed two groundwater monitoring wells on the property. Data obtained from these investigations indicated that contaminants were present in soil and groundwater on the property at concentrations exceeding applicable MTCA soil and groundwater cleanup levels in several locations.
Prior to commencing with the Remedial Action (RA), RGI conducted a Pre-Demolition Hazardous Materials Survey at the property in order to assess building materials in the existing buildings prior to demolition. In addition, RGI obtained a Contained-In determination from the Washington Department of Ecology (Ecology), which allowed for soil containing concentrations of PCE below the threshold value to be disposed of as non-hazardous, which reduced soil disposal costs.
During the RA, RGI identified and decommissioned five underground storage tanks (USTs) and one septic tank in accordance with applicable regulations. The most significant impacts were observed beneath a leaking heating oil UST on the western portion of the property, which RGI determined had been inappropriately used to store spent solvent from the dry cleaning facility. Diesel and PCE impacted soil extended to depths up to 40’ bgs in this location.
RGI directed the remedial excavation of contaminated soil from seven separate locations on the property and analyzed performance and confirmation soil samples to guide remedial excavations and confirm that the limits of each excavation were in compliance with MTCA regulations. Contaminants encountered in soil and remediated during the RA included petroleum-related contaminants, metals, and dry cleaning solvents.
RGI coordinated with the general contractor (GC) and utilized the data obtained during previous subsurface investigations to strategically plan remediation of soil and groundwater impacts encountered on the property in conjunction with the redevelopment of the property. This included completing a portion of the remedial excavation in a given location during each successive lift of the mass excavation, which allowed mass excavation to move forward efficiently. RGI also utilized onsite mobile laboratory services, when appropriate, to analyze samples in real time, which minimized delays to construction activities due to waiting for analytical results.
Remedial excavations were completed to the maximum depths feasible throughout the Property and it was necessary to excavation be beneath the redevelopment subgrade at 23’ bgs to remove contaminated soil form one area on the western portion of the Property. In this location, the remedial excavation was completed via a series of slot excavations under the supervision of an RGI geotechnical engineer. Slot excavations were designed to protect the integrity of the west shoring wall and consisted of completing a series of trench excavations perpendicular to the west shoring wall and backfilling these locations with CDF. Once the CDF was given appropriate time to set, slot excavations were completed between the CDF backfilled areas and backfilled with CDF. All contaminated soil was excavated to the maximum depth feasible of 32’ bgs as determined by the geotechnical engineer. However, it was necessary to leave contaminated soil in place at depths up to 40’ bgs in two locations on the southwestern portion of the Property as deeper excavation in these areas may have jeopardized the integrity of the western shoring wall
A total of 1,434 tons of soil were removed from seven locations across the property to depths up to 32’ bgs. Approximately 1,340 tons of petroleum contaminated soil (PCS) and soil containing concentrations of PCE below the MTCA soil cleanup level were removed from the Property and disposed of at the CEMEX disposal facility in Everett, WA. An additional 94 tons of PCE-impacted soil were removed from the property and disposed of as non-hazardous under a Contained-In determination obtained from Ecology at the Republic Services disposal facility in Seattle, Washington.
Upon completion of remedial excavations, diesel-range TPH and benzene were present in groundwater exceeding applicable MTCA groundwater cleanup levels. RGI installed and sampled two additional groundwater monitoring wells during redevelopment. These wells were located on the southwestern portion of the property in the footprint of the parking garage and were used for compliance monitoring. These wells were also designed to facilitate chemical injections, which were later determined not to be necessary.
All the work completed during the Remedial Action was documented in the Remedial Action Report, which was submitted to Ecology for review under the Voluntary Cleanup Program (VCP).