Excavating and Removing Nearly 300 Tons of Contaminated Soil to Protect Groundwater

The primary objective of this project was to remove as much impacted soil as possible, including all vadose zone soil exceeding State of Florida Cleanup Target Levels (CTLs) to prevent further impacts to groundwater quality.

Setting up the Slide Rail System

Due to the depth of the excavation and proximity to the right of way, shoring was required to complete the excavation. The shoring system selected for this project was the GME Modular Slide Rail System, which allows for shoring to be installed as the dig progresses. The Slide Rail System is an engineered modular system that consists of rails, panels, and struts that are assembled within the ongoing excavation.

Slide Rail Installation

On February 18, 2014, soil excavation and slide rail installation was initiated. Prior to beginning the shoring system assembly, a 4-foot deep pilot hole was required. The shoring location and excavation limits were determined based on the previous boring locations, which were identifiable in the field. The pilot hole was excavated, and the on-site assembly of the slide rail components was completed.

On February 19, 2014, the assembly of the shoring system within the excavated pilot hole was initiated.  Shoring installation began with the western corner posts and panels, progressing to the east. The slide rail system consists of interlocking posts and panels, which are assembled in the 4-foot-deep pilot hole and then pushed downward as the excavation progresses. Once the first row of panels has been lowered to the point where the top of the panel is near the ground level, a second row of panels is set above the first and again pushed down as the excavation progresses. Water infiltration was observed at a high rate beyond 10 to 10.5 feet below land surface (bls). Significant water infiltration around the shoring system can cause a washout of soils outside of the shoring, rendering the shoring ineffective. Therefore, the excavation was terminated at a depth of 10 to 10.5 feet, due to the water infiltration and undermining concerns. The shoring system installation was completed by the end of the day on February 19, 2014.

Excavation Summary

The excavation was completed on February 19, 2014. Excavation was advanced to a depth of approximately 10 to 10.5 feet throughout the majority of the excavation, based on a distinct lithology change, beyond which water infiltration became substantial. The lithology at this depth transitioned from a plastic, sandy clay to a medium to fine sand. The sandy clay layer appeared to be highly impacted, which correlated with prior site assessment data.

On February 19 and 21, a total of 277.19 tons of impacted soil was loaded for offsite disposal.

Slide rail system components were removed concurrently with the backfilling of the excavation area on February 20 and 21.