Up a winding canyon road in the foothills near Kittredge is where Flatiron Constructors Inc. and ASI Constructors Inc. built the new Genesee Dam No. 2 the state's sixth largest water treatment facility to be constructed this year.

This new dam is comprised of roller-compacted concrete poured in one-ft lifts. RCC is coarse and moist, like crumbly mud, and challenging to work with because it lacks the viscosity of typical concrete. The team blasted, crushed and mixed the RCC onsite. Once mixed, the RCC was placed on a conveyor belt and dumped into a haul truck at the top of the dam. The truck placed the RCC directly onto the dam, where a small bulldozer spread the crumbly mixture over the entire surface. A sensor attached to the bulldozer notified the operator when the layer became level, and then the surface was ready for another batch of material.

RCC does not require the testing of slumps and breaks, but instead needs density testing to determine the integrity of the material. RCC also cures quickly, so once it’s placed, leveled and compacted, the team could immediately place more RCC on top.

The joint venture team began placing and compacting the RCC in November 2006 and worked 21 days straight to place 40 lifts. A total of 34,500 cu yd was required to construct the 90-ft-tall dam, which holds 100 acre-ft of water.

The team weathered two major storms that dumped a total of about 50 in. of snow on the project, and in mid-January, daily high temperatures stayed below 10 degrees for a stretch of four days. The cold temperatures made it impossible to pour RCC, which requires a minimum temperature of 24 degrees. Despite this, the project remained on schedule, with final testing of the dam conducted in fall 2007.

Genesee Dam No. 2
Kittredge

Silver Hard Hat Award

With expanding Front Range communities facing foreseeable water shortages, Parker Water and Sanitation District developed plans for the 16,000-acre-ft Rueter-Hess Dam and Reservoir. Phase one construction on the $105-million project began in 2004. 

SEMA Construction performed the phase-one earthwork, which involved construction of a mile-long zoned, earthfill dam containing over 6.6-million cu yd of fill borrowed from the reservoir basin; foundation preparation of the 70-acre dam footprint; internal drainage systems; structural excavation and backfill of the 1,500-ft-long outlet works; and 84,000 cu yd of soil-cement dam face protection. 

The zoned fill dam presented special construction challenges, including working with six different types of fills, all with differing soil classifications. An additional challenge included being responsive to the redesign of the embankment zone geometry to accommodate a future, enlarged-dam configuration. 

Non-stop coordination among field personnel ensured that excavated material was properly processed, classified and placed in the correct fill locations. Building the dam’s foundation core cut-off trench and buttress fill shear keys required extensive foundation dewatering of the valley floor using 15 deep dewatering wells, numerous localized well points and sumps and an interceptor cut-off trench to control groundwater within Newlin Gulch. 

A cofferdam and diversion system capable of handling a 100-year storm was built to keep water from the seasonal Newlin Gulch Creek out of the work area. Several storms approaching this magnitude occurred during construction, and the cofferdam performed flawlessly. SEMA also encountered some significant archeological sites that required close coordination and historical preservation efforts. 

Rueter-Hess Dam
& Reservoir, Phase I
Parker

Bronze Hard Hat Award

The South Fort Collins Sanitation District has been one of the fastest growing service providers in Northern Colorado, with annual tap sales hitting 1,000 in recent years. To meet this rapid growth, the district has upgraded and expanded its existing treatment system (capacity of 3 million gal. of wastewater per day) several times, but it cannot be expanded again economically and does not use the latest technologies available, so the system is rapidly approaching the end of its useful life.

In 2005 the district decided to build a new expandable wastewater treatment facility with an initial capacity of 4.5 mgd. The second phase of the project increases the total capacity to 9 mgd, enough to provide service through full build-out within the district. The first phase includes an Orbal® oxidation ditch, an extended aeration system followed by final clarification, effluent filtering and disinfection using an ultraviolet light system.

The plant also incorporates an innovative technology known as the Cannibal® Solids Reduction Process, developed by U.S. Filter’s Envirex Products. The Cannibal system includes both physical removal and biological conditioning of solids that all but eliminates routine sludge wasting. The system should greatly reduce operations and maintenance costs associated with solids handling.

Construction of the $21-million design-build project started in March 2006 and was completed in fall  2007. The general contractor, selected through a prequalification process, proposed a guaranteed maximum price and shared cost savings based on 70% complete design drawings prepared by TEC. The team approach among the owner, engineer and contractor expedited and economized design and construction the project finished ahead of schedule and under budget.

South Fort Collins Sanitation District
Wastewater Treatment Plant
Fort Collins

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