Abstract:
To aid in the redevelopment of the former Time Oil Bulk Terminal facility in Seattle, WA, Forgen performed treatment of contaminated soil to address source area soil with indicator hazardous substance and LNAPL. This paper will focus on the collaboration between Forgen and the engineer to develop a mixing technique with conventional equipment allowing treatment up to 40’ bgs.
Forgen provided constructability review services to the Engineer throughout the design process. Forgen and the engineer initially proposed auger mixing due to the required treatment depth. However, after the engineer performed geotechnical investigations, Forgen recognized that without performing a pilot test, the desired in-situ treatment goals may not be achievable with that method of ISS. The timeline and budget for this project did not allow a pilot study to be performed due to the high mobilization cost of equipment so excavator mixing was recommended by Forgen. A portion of the site perimeter along an operating rail line required treatment to a depth of 40’ , which was beyond the reach of the Cat 390 excavator proposed for the mixing. With the impacts up to the site perimeter, it’ s not possible to slope or bench down to allow the excavator to reach the treatment depth. A shoring wall was installed along the site perimeter as excavation support; then Forgen excavated and relocated the top 10’ of contaminated soil to a nearby stockpile location where that material would be mixed ex-situ. To achieve the remediation goals without compromising the integrity of the shoring supports, Forgen performed in-situ mixing in small 8’ x20’ cells treated in a piano key fashion up against the shoring wall.
Forgen completed the treatment of the 30, 000 CY of impacted soil at the site on schedule and within budget, leaving the property successfully cleaned up and thereby allowing redevelopment to proceed.