Significant Project Features:
- Deep PRB installation via the Soil Mixing Method
- Drilling through deep unconsolidated sand
- Bio-polymer slurry utilized as a drilling fluid
- Installation of the proprietary reagent BOS-100 as provided by Remediation Products Incorporated
- Project completed in an environmentally sensitive area
Background:
Vandenberg Air Force Base is located adjacent to Lompoc, California and is utilized by the federal government for the Department of Defense space and missile testing program. The Air Force Center for Engineering Excellence (AFCEE) tasked Geo-Solutions’ client, with the installation of a permeable reactive barrier to mitigate chlorinated solvent contamination in the groundwater in the north base area. The contaminant present in the groundwater and soil in this area is due to releases from government operations.
A permeable reactive barrier is an underground installation that, when complete, leaves behind a permeable lens. This lens is oriented so that potentially contaminated groundwater will flow through. The addition of an environmental reagent to the permeable lens creates a matrix by which the contaminated groundwater undergoes remedial action. In this case the permeable lens was installed by mixing the sand already present with the proprietary reagent, BOS-100 manufactured by Remediation Products Incorporated. The BOS-100 was dispersed throughout two subgrade alignments utilizing the shallow soil mixing method.
Geo-Solutions designed and constructed the PRB, making good advantage of our expertise in soil mixing methodologies. Work on this project took place in two distinct alignments. In the first area, soil mixing took place to approximately 71-feet below grade. In the second area, the soil mixing was completed to 50 feet below grade. Both alignments were completed with a Soilmec 930 drill rig. Work was completed utilizing bio-polymer slurry both as a drilling fluid and as a vehicle for the installation of the BOS-100. The slurry has the proper physical characteristics for both tasks and is easily metabolized to a viscosity near that of water via a simple enzymatic reaction. The slurry percolates naturally along with the ground water at the site once metabolized.
Of particular note, is the area in which the project was completed. It is one of the few remaining habitats of the El Segundo Blue Butterfly. Work was scheduled outside the butterfly’s mating season to protect this endangered species. The challenge in completing this project was avoiding the El Segundo Blue’s primary source of nectar the Dune Buckwheat plant. Dune buckwheat was interspersed throughout the project site. Geo-Solutions’ field crews successfully avoided damage to any of the plants. Work on this project was projected on a fast track schedule and completed accordingly.
Project Objectives:
- Placement of the PRB matrix perpendicular to and encompassing the flow of the main body of the aquifer it was designed to treat.
- Achievement of a stable sand and reagent matrix placed at the optimum position to intersect groundwater.
Description of Work:
- Two PRB alignments each 50 feet long, one at 71 feet deep and the other 50 feet deep.
- Approximately 22,000 Vertical Square Feet.
- Backfill material consisted of natural sand and a proprietary reagent.
- Low permeability was maintained throughout the PRB matrix per design.
- Geo-Solutions completed this effort as a design-build project.
Project Challenges:
- Soil-Mixing in ecologically sensitive area.
- Soil Mixing progressed through a very high water table at the site.
- Fast track scheduling was required by Geo-Solutions’ client.
