Project Features:
- In-Situ Soil Mixing (ISS) by excavator/rotary blender system method
- 47,000 Total Cubic Yards (CY) at up to 27-feet in depth
- Target of 50 psi Unconfined Compressive Strength (UCS) and Permeability of 4.0E-06 cm/sec
Background:
The Atlantic Wood Industries (AWI) site consists of approximately 48 acres of land on the industrialized waterfront of Portsmouth, Virginia, and 30 to 35 acres of contaminated sediments in the Southern Branch of the Elizabeth River. From 1926 to 1992, a wood-treating facility operated at the site using both creosote and pentachlorophenol (PCP). At one time, the Navy leased part of the property from AWI and disposed of waste on site, including used abrasive blast media from the sand blasting of naval equipment and sludge from the production of acetylene. Polynuclear aromatic hydrocarbons (PAHs), PCP, dioxins and metals contamination (mainly arsenic, chromium, copper, lead and zinc) have been detected in soils, ground water, and sediments. EPA issued a Record of Decision in 1995 for the cleanup of the site, which was amended in 1997. The AWI Site was added to the National Priorities List of most hazardous waste sites in 1990.
Project Objectives:
Geo-Solutions was contracted by the Norfolk District of the US Army Corps of Engineers to perform Phase 1B of the cleanup effort which included the stabilization and solidification of over 47,000 CY of DNAPL-impacted soils.
Description of Work:
The Treatment Area, or Historic Disposal Area (HDA), consists of 29 separate cells ranging in depth from 8 feet to 27 feet below ground surface. Due to the amount of debris expected throughout the HDA, GSI selected the excavator/rotary blending ISS system to perform the stabilization of the DNAPL-impacted soils. This system combines the use standard hydraulic excavators with an excavator-mounted rotary-blending unit to homogenously blend the subsurface soils with the chosen reagents.
The impacted soil was blended with a cement-based liquid grout consisting of:
- Portland cement
- Ground granulated blast furnace slag cement
- Organophilic clay
Two separate mix designs were selected for the project depending on the section being mixed. Each mix design was to attain a minimum UCS of 50 psi and a maximum permeability of 4.0E-06 cm/sec.
GSI served as the prime contractor for the project. The scope of work for the project also included:
- Relocation of electrical utilities for the neighboring Portsmouth Public School District Property to accommodate soil mixing.
- Perimeter air monitoring
- Pre-excavation, removal, handling and stockpiling of over 3,000 CY of miscellaneous debris.
- Final grading
- Installation of an impermeable clay cap.
- Restoration
Project Upgrades:
- Perimeter Naphthalene sampling frequency increased to daily
- Level of protection upgraded to Level C for majority of project due to suspect air monitoring results
- Personnel TWA sampling performed to supplement PID-based air monitoring
- Odor-control foam applied during ISS operations to help control VOC’s.
