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Siebring Reservoir


Greeley, CO

Hall Irwin's (and North America's) first slurry wall around a gravel pit! In 1990, we cooperated with Deere & Ault Consultants in this Design-Build project, creating the original soil-bentonite cutoff wall installation process with custom machinery built to execute each step.

This process solved the decades-long problem of evaporation and un-metered groundwater infiltration, which the State of Colorado sought to put a stop to with laws passed in 1977. The process also facilitates dry excavation of gravel pits without water seepage, and in essence creates an underground clay "bowl" for storing water after mining is complete.

Our team installed two different slurry walls at this site to an average depth of 33’, totaling 10,000 LF of slurry and providing approximately 1,800 acre-feet of water storage. The first wall surrounds the western three cells, while the second was installed at a later date and surrounds the easternmost cell. We built an interconnect between the two cells, with a 5-CFS pump station to convey water out to the river and a diversion structure to bring water back from the river during the spring. More than 30 years later, the Central Colorado Water Conservancy District (CCWCD) still benefits from these water storage cells.

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