Mine Reclamation & Water Storage Reservoir

Denver Water is the oldest and largest water utility in Colorado. They serve 1.4 million people in Denver and nearby suburbs. Denver Water bought the Lupton Lakes Reservoir site. This site was formerly a series of gravel pits resulting from sand and aggregate mining. The goal was to convert these pits into water storage reservoirs.
 
Upon acquisition, the site lacked essential components for reservoir functionality, such as hydraulic infrastructure, groundwater control, and stable reclamation slopes. The project aimed to meet the State of Colorado Engineers Office Gravel Pit criteria established in 1999. Ultimately, the goal was to create a water storage reservoir capable of storing over 3,000 acre-feet of water.

The project involved two main components: constructing a soil-bentonite slurry wall for water storage containment, groundwater control, and reclaiming previously mined high-wall slopes. Forgen collaborated with Deere & Ault Consulting, Inc. of Longmont, Colorado. We began with an initial conventional design during the RFP stage and progressed through design phases to finalize the cutoff wall construction at 30%, 60%, 90% and 100%. 

Design activities included permit research, SWPPP development, drilling programs, topographical surveys, slope stability analysis, and final design reports. The soil-bentonite slurry wall, constructed over two seasons, utilized two PC 1250 Komatsu Excavators with extended arms capable of reaching depths exceeding 80 feet. 

We installed a total of 515,000 square feet of slurry wall. Depths reached up to 60 feet, with an average depth of 57 feet. Tasks included clearing and grubbing, constructing temporary platforms, maintaining dewatering at 7,000 gallons per minute, and coordinating with the mine operator. We also installed temporary fencing. Forgen also successfully installed the soil-bentonite wall around existing underground utilities.

Additionally, Forgen partnered with Denver Water for the design and construction of reclamation slopes for the previously mined high-wall and pit floor areas. This effort included detailed design work using existing soils/spoils, bedrock floor, available mine complex soils, and imported materials to stabilize the slopes.

A variety of equipment placed over 1,030,000 cubic yards of zone fills. This included a fleet of ten (10) 627 scrapers, excavators, 815 compactors, GPS-enabled dozers, and motor graders, along with supporting equipment. The reclamation work involved preparing the foundation for embankment placement up to 10 feet into claystone bedrock. 

Site restoration activities included constructing a rim road around the newly constructed water storage reservoir, replacing perimeter fencing, restoring drainage features, and seeding slopes to complete the geotechnical construction project.

The installed soil-bentonite slurry wall exhibited a hydraulic conductivity of 1 x 10^-8 cm/sec, meeting the design requirements for lining gravel pits. This ensured effective water storage containment and groundwater control. The multi-disciplinary project brought together a team in partnership with the owner to successfully complete the lump sum project on time and within budget, without any recordable injuries.

Denver Water recognized the project with the 2017 Project of the Year award for its exemplary execution and environmental remediation efforts. This success in reservoir construction was achieved using alternative delivery methods.