Significant Project Features:
- Site Remediation with the use of Zero Valent Iron (ZVI) and Bentonite;
- Used backhoe and Alpine rotary mixing tool for mixing depth of 17’ below the work platform through dense clayey soils
- Restricted work area below surrounding ground surface
- Project site was surrounded by a populated neighborhood and school zone.
Background:
Geo-Solutions completed an in-situ Chemical Reduction (ISCR) project at a former maintenance, fueling and storage of oil field equipment site. The site is surrounded by a populated neighborhood in the City limits of Gillette Wyoming.
The work included the soil mixing of 13,476 cubic yards of Benzene, Ethylbenzene and Chlorinated volatile Organic Impacted soils from 0-17 feet below a prepared work platform. A specified dry addition blend of 2.0% ZVI and 1.48% Bentonite Clay were delivered to the site and stockpiled until needed. Soil mixing was performed with a standard CAT 336 excavator, standard CAT 329 long reach excavator, and modified CAT 336 excavator with an Alpine rotary mixing head attachment.
The working platform was prepared by removing and stockpiling the top 3 feet of clean soil below the existing ground surface. Soil burritos, silt fencing, mix zone swell containment berms, and a site haul road was also installed part of the site preparation.
Soil mixing was divided up into individual cells with dimensions typically 10×20 feet, while perimeter cells varied in size and shape to ensure 100% coverage of the mix area.
While the spatial limits of the soil mixing area were the biggest challenge with this project, managing the high specified quantity of dry reagent was key to this particular project. Significant volumes of clean water were required to facility the breakup and proper distribution of the reagents.
Additional challenges were the wet ground conditions, further exacerbated by the limited working area, high groundwater table, Late Fall weather and limited available daylight.
While the iron reagent addition limit was specified to be between 1.0% and 2.0% by weight of soil, Geo-Solutions was responsible for overall quality control of the soil mixing activities which included process controls to ensure accurate reagent blending and reagent addition rates. The horizontal and vertical limits of the ISCR work were verified by total station survey equipment during execution of the work.
Project Objectives:
- Clear and grubbing the site.
- Relocation of site entrance/exit.
- Installation of the construction haul road.
- Site access gates.
- Stockpiling and covering the top 3 feet of clean soil in the soil mixing area.
- Excavation and disposal of 3,205 tons from the excavation hot spot zone
- Perform soil mixing of 13,476 cubic yards. Meet the performance standards of 1.0%-2.0% ZVI and minimum of 1.48% Bentonite clay reagent addition.
- Capping of the soil mixing area.
Project Challenges:
- Limited work area with several large pieces of equipment constantly working.
- Limited material storage area.
- Demobilizing after soil mixing work was completed and returning in the winter to perform capping when the soil mixing area was frozen. As with any soil mixing application with non-cementicious materials, physical strength was lacking after mixing to support loading.
