Cheyenne, WY: Containment Wall and Groundwater Extraction Trench

Cheyenne, WY: Containment Wall and Groundwater Extraction Trench

Project Description

Soil-Bentonite (SB) Slurry Wall, Bio-polymer (BP) collection trench
Vulcan PERC SBCW Project
Cheyenne, Wyoming

Significant Project Features:

• Soil-Bentonite Slurry Wall
• Bio-polymer Slurry Wall
• Upgrades to existing groundwater treatment facility
• SBCW: 1348 Linear Feet. 64,849.7 Square Feet. Maximum of 50.5-feet deep
• GWET: 232 Linear Feet. 10,021.0 Square Feet. Maximum of 48-feet deep
• Target Average Permeability of 1 x 10-7 cm/s

Project Objectives:

Geo-Solutions, Inc. (GSI) was contracted by Union Pacific Rail Road to install the Soil-Bentonite Containment Wall, the Groundwater Extraction Trench, and the upgrades to the existing groundwater treatment system. These measures were designed to contain, collect, and treat potentially impacted groundwater at the site.

Description of Work:

GSI initially pre-cleared the top 10 feet of the trench alignments using an excavator and demolition hammer. Included in this work were the removal of asphalt, concrete, abandoned utilities, and structures related to previous rail yard work. Structures of reinforced concrete were encountered at depths up to 17 fbgs, and contained a variety of fill material including bricks, liquid (disposed of by others), and discarded rail yard materials. A variety of known and unknown, active and abandoned utility lines were encountered in the alignment. Active utilities, including a natural gas line, were relocated or protected.

The SBCW included the installation of a 30-inch wide by 65,000 vertical square feet (vsf) soil/bentonite (SB) slurry wall. The wall was installed to a maximum depth of 50.5 feet below ground surface (fbgs), to the depth prescribed by the Engineer.

Excavation was accomplished under bentonite slurry using GSI’s Komatsu PC800 excavator outfitted with a standard boom and long-stick attachment. Bentonite slurry for trenching was produced on site in GSI’s custom-made batch plant and pumped to the trench. The SB wall was 1,348 linear feet and encircled the UPRR turntable.

Trench spoils were loaded into off-road articulated trucks and hauled to a remote mixing location where they were temporarily staged in a lined holding pit. The spoils were passed through a 3” mechanical screen to remove oversized material, then loaded into a lined mixing pit. The spoils were blended with bentonite slurry as well as additional dry bentonite in measured batched to create a homogenous mix which became the SB wall backfill. The target permeability for the SB wall was an average of 1 x 10-7 cm/s. Target permeability was surpassed in all samples with an overall average permeability of 3.2 x 10-8cm/s.

The Groundwater Extraction Trench (GWET) included the installation of a 30-inch wide by 10,000 vsf trench installed by the Bio-polymer trenching method. The wall was installed to a depth of 45 fbgs, with the well sump at a depth of 48 fbgs. The GWET is located within the alignment barrier wall, and will collect the impacted water. An electric submersible pump was installed in the well sump and the end of the GWET.

Excavation was accomplished using a cellulose-based polymer slurry. GSI used our Komatsu PC800 excavator outfitted with standard boom and a long-stick attachment. Bio-polymer slurry for trenching was produced in GSI’s custom made batch plant and pumped to the trench.

Trench spoils were loaded onto articulated dump trucks and transported to a lined pit for later characterization and disposal. The trench was backfilled with #67 gravel backfill.

Geo-Solutions served as the prime contractor for the project. The scope of work for the project also included:

• Completion of Pre-mobilization submittals;
• Mobilization to the Site of equipment, personnel, and materials necessary to begin the work;
• Completion of One Call and UPRR utility clearances, as wells as an independent locator;
• Erosion and Sediment Control installation and general site preparation;
• Removal of concrete and asphalt;
• Pre-Clearing of underground structures within the trench alignments to 10 fbgs;
• Quality Control (QC) testing related to the SBCW and Extraction Trench;
• Restoration of utilities;
• Stabilization, characterization, and off-site T&D of impacted trench soils;
• Stabilization, characterization, and off-site T&D of construction debris (asphalt, concrete, bricks, RR ties, etc.);
• Development of the GWET well, including characterization and treatment of the impacted water with activated carbon vessels;
• Site Restoration including the
o Stabilized track areas, using Geo-Grid and compacted sub-ballast layers
o Asphalt paving of areas disturbed during trenching
o Gravel surfaces;
• Industrial Waste Water Treatment Facility upgrades; and,
• Demobilization from the Site of equipment, personnel, and exc