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Hydraulic Isolation of Lagoons or Holding Ponds

Weld County, CO: Bayshore Ponds, Soil-Bentonite Slurry Wall


Geo-Con completed the installation of a slurry wall system around a former gravel pit and future reservoir near Firestone, Colorado. The reservoir is part of a residential development and used for recreation and irrigation water storage. Geo-Con was contracted by the owner on a design-build basis for this project.

The design was completed by Geo-Con along with a subcontracted engineering firm. The design considerations included the permeability of the slurry wall in conjunction with the seepage of the bedrock. A SEEP-2 analysis was completed to determine the total key-in depth. The design also considered the slightly higher permeability in the required Soil-Cement-Bentonite (SCB) sections and numerous utility penetrations. At the completion of the installation, Geo-Con and its engineer completed the monitoring and certification of the slurry wall performance per the State of Colorado 90-day leak test requirements

The total slurry wall installed is approximately 390,000 square feet, with depths varying from 19 to 36 feet. The total length of the wall is approximately 14,000 feet. The wall is keyed 7 feet into the underlying Denver Formation Blue Shale layer. Geo-Con created backfill with trench spoils along with dry bentonite to achieve permeability in the range of 1x10-8 cm/sec. This low permeability is required to meet the State of Colorado Engineer's Office requirements for leakage in this type of water storage system. The slurry wall also includes five soil-cement-bentonite sections. These SCB sections were included in the design for added stability and erosion protection for future spillways between the St. Vrain River and the reservoir.

In addition to the slurry wall, Geo-Con's design-build work included the following:

  • Structural cap of the slurry wall.
  • Installation of 8 new utility penetrations through the slurry wall. These utility penetrations will be used for the future diversion structure and pump house facilities.
  • Protection of and excavation around 6 existing utilities (municipal water, natural gas, and petroleum pipeline).
  • Removal of sandstone in the slurry trench alignment using a trenching subcontractor.

The significant challenges on this project included working continuously through the winter months, the utility penetrations, and working in narrow areas between the reservoir and the St. Vrain River.


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