Antea Group’s approved remedial action plan included advancing large diameter auger (five feet) boreholes throughout the pre-identified area of soil impact. Large diameter auger excavation was selected due to the limited size of the site, the depth of impacted soil which represented a barrier to closure, and the ability to execute precision excavation without extensive shoring or sloping. Five boreholes were advanced to 30 feet (ft) below ground surface (bgs) and 52 boreholes were advanced to 35 ft bgs.
In order to keep the boreholes open during advancement, a polymer slurry was utilized to stabilize the sidewalls. Upon reaching the target depth for each borehole, high strength concrete was installed to a depth of six feet bgs. Above six feet bgs, a low-strength concrete was used to accommodate future property redevelopment.
To achieve full removal of soil within the targeted area, each borehole location was predetermined and marked with a high precision global positioning system (GPS) antenna. At the end of each workday, borehole locations were remarked to ensure that disturbances caused by the execution of site work did not interfere with borehole location documentation. Since each borehole was backfilled with concrete which needed time to cure before advancing a neighboring borehole, Antea Group used a Python coded algorithm to determine the order of borehole advancement.
The algorithm ensured that each day’s work would occur greater than ten feet from a borehole that had been backfilled within the last 48 hours. This prevented collapse of a previous day’s concrete backfill into a new borehole. Following site work each day the Python algorithm was updated to account for actual work completed and accommodate adjustments to the borehole order of execution, as necessary.
