Project Description

RGI was retained to assess an oil like substance discovered by construction personnel in the sub-basement of a building undergoing renovations in Seattle, Washington. The sub-basement was approximately 27 feet below street grade and three floors down in the building and the only access to the sub-basement was a standard sized door. Therefore, the project created unique and complex challenges, which required RGI’s innovative problem solving skills and a network of RGI professionals including skilled experts in the areas of environmental science, engineering, geology, hydrogeology, and vapor intrusion. The project also required utilizing RGI’s vast network of skilled subcontractors (utility locators, concrete coring, excavation, structural engineer, vacuum excavator, environmental laboratory, forensic chemist, marine chemist, UST decommissioning, tank cleaning, and limited access and hollow stem auger drilling) to successfully complete the work required for this project .
RGI’s initial assessment identified the presence of Bunker C oil and diesel-range total petroleum hydrocarbons (TPH) in the sub-basement. RGI subsequently conducted further investigations, which included retaining Mr. Phil Duos (Geophysicist) to conduct a geophysical survey in the sub-basement, which led to the identification of two 8,500-gallon underground storage tanks (USTs) situated approximately 5 feet below the grade of the sub-basement (or 32 feet below the street grade).
RGI conducted a review of all previous reports and historical documentation for the Site and there was no documentation regarding the discovered. However, RGI completed a historical review, which revealed that the USTs were likely installed in the early 1900’s and associated with a former steam heating plant that was situated on the south-adjoining parcel.
Prior to proceeding with the UST decommissioning, it was necessary to perform additional services as part of preparation for UST decommissioning in order to make the work area safe, prevent any potential spreading of contamination and provide equipment access to the sub-basement. These services consisted of re-routing a leaking water line that extended across the sub-basement, removing a significant amount of debris in the area of the USTs, acquiring the necessary permits for decommissioning of USTs, notifying the Department of Ecology, obtaining a permit for street use for parking for multiple contractor vehicles and staging equipment, coring concrete holes through two floors in order to run lines from subcontractor vehicles and equipment staged on the street to the sub-basement work area, running a ventilation hose from the sub-basement to the outside to remove vapors from the work area, profiling the product in the USTs, coordinating waste disposal with disposal facilities, and bracing the top of the USTs against the ceiling with pole shores under the supervision of a licensed structural engineer. The bracing was necessary in order to counteract any buoyancy force that could result when the contents of the USTs were removed since the bottom of each UST was situated in groundwater.
RGI retained IO Environmental & Infrastructure (IO), a certified UST Decommissioner, to complete the UST decommissioning. The work commenced with utilizing hand digging tools to remove the approximately 5 feet of soil above the USTs and determine the orientation of each UST. A certified UST Assessor from RGI then sampled the contents of each UST and measured how much product/water was contained in the USTs.
The next step in the UST decommissioning process consisted of utilizing an electric saw to cut access ports on the top of each UST with the oversight of a Marine Chemist to ensure conditions were safe and there was no risk of explosion. Approximately 17,000-gallons of oil/water were then pumped from both USTs to a vacuum truck operated by Marine Vacuum Services, Inc. (Marvac) parked on the street. The USTs were determined to be constructed with one quarter inch riveted steel and the interior of each USTs contained three baffled chambers. The riveted construction of the USTs confirmed RGIs conclusion that the USTs were installed in the early 1900’s based on the historical review and the preliminary forensic evaluation since riveted construction of USTs ceased around 1920.
After all product was removed from the USTs, RGI oversaw the cleaning and rinsing of the inside of the USTs, which was also completed by Marvac personnel entering the USTs to clean and rinse the inside of the USTs soap and a pressure washer. The cleaning and rinsing of the USTs occurred over a period of approximately 2 weeks and a total of approximately 6,500-gallons of oily water were pumped from the USTs up through the building and outside to the vacuum truck.
RGI conducted an interim remedial action in conjunction with the UST decommissioning which consisted of RGI Drilling, Inc. installing four 4 inch product recovery wells in the immediate vicinity of the USTs. It was not possible to mobilize drilling equipment to the sub-basement, therefore RGI installed these wells by retaining Lavelle Vac, Inc. (Lavelle) to utilize a vacuum truck to vacuum excavate soil from the sub-basement to a vacuum truck at street level in four locations. Due to the high amount of wood debris in the subsurface, it was necessary to use a telescoping pole pruner to saw cut wood encountered in the boreholes during vacuum excavation. The wells were screened to intersect the saturated/unsaturated interface by a licensed driller. The wells were developed and later utilized to remove contaminated groundwater and LNAPL from the UST excavation. A total of approximately 1,850-gallons of sludge consisting of contaminated soil and groundwater were transported off-Property for disposal in accordance with applicable regulations by Lavelle.