Red Willow Dam Modifications

Company: SEMA Construction, Inc.
Industry: Water/Wastewater
Location: McCook, Nebraska
Expected Completion Date: November 29, 2013
Project Website

Located north and upstream from the town of McCook, Nebraska, the Red Willow Dam impounds water to create Hugh Butler Lake and serves primarily as a regional flood control/irrigation reservoir and state park recreational facility. This water resource project provided safety modifications to a large reservoir operated by the United States Bureau of Reclamation (USBR). The Dam historically experienced unsatisfactory seepage through the dam slope and associated downstream slope instability, which posed a serious dam safety concern for downstream communities.

SEMA Construction, Inc. (SEMA) was the General Contractor selected for this 15 million dollar project. The principal components of construction included: excavation of 400,000 cubic yards from the entire downstream face of the embankment to the top of the existing sand blanket for major embankment reconstruction; removal of the existing toe drain and seepage monitoring system and extending the existing sand blanket to an improved toe drain seepage management system; placement of geonet composite on the excavated embankment slope for seepage control; construction of a new, two-stage filter chimney drain zone to capture and manage future seepage; reconstruction of a more stable embankment slope that included a downstream stability berm and buttress and reconstruction of the discharge basin below the spillway and outlet works.

The superior partnership between SEMA and USBR was evident throughout the course of pre-planning and construction, and key to the successful result. SEMA is proud of the “outstanding” ratings received from the USBR in Cooperation and Responsiveness, Correction of Noted Deficiencies, and Effectiveness of Job-Site Supervision.

The entire project team is pleased with the seven-month early completion of this complex water resource project, but mostly, that this vital multi-use facility is environmentally sound and operating safely.

What impact does this project have on America?

The Red Willow Dam Modifications had a significant impact on the people and environment of the State of Nebraska. Commissioner Connor said… “This investment will ensure Red Willow Dam will continue to serve the people of Nebraska and the nation for future decades. This contract helps us restore one of our key structures and helps create job opportunities.” The dam provides water for recreation and irrigation purposes.

What interesting obstacles or unusual circumstances did you overcome to complete the project?

The unusual circumstance that was managed in the Red Willow Dam Project was its location in a state park and wildlife area; environmental protection was a key goal. Because of the unique project location and potential habitat for threatened species, SEMA and the USBR were required to conduct preconstruction and ongoing surveys for Bald Eagle and Kit Fox activity in the project limits.

SEMA developed a Pollution Prevention Plan (PPP) that fulfilled environmental compliance requirements of the State of Nebraska, Nebraska Department of Environmental Quality and USBR submittal requirements. The PPP outlined specific measures related to storm water, site and construction activity and controls to reduce pollutants including a sequencing schedule for all best management practices (BMPs).

SEMA’s professional engineer and environmental compliance officer developed a Storm Water Pollution Prevention Plan (SWPPP) for Red Willow Dam.

The SWPPP provided a description of every potential pollution source and associated site-specific description as well as prevention practices for each. These sources included: disturbed and stored soils, vehicle tracking of sediments, management of contaminated materials, loading and unloading operations, outdoor storage activities (building materials, fertilizers, chemicals, etc., vehicle and equipment maintenance and fueling, significant dust or particulate generating processes, activities involving fertilizers, pesticides, detergents, fuels, solvents, oils, etc., and onsite waste management practices (waste piles, liquid wastes, dumpsters, etc.).

BMPs that SEMA developed for storm water pollution minimization/reduction included: silt fence, slope tracking/soil roughening, erosion control berm/diversion, check dams (hay hale, earthen, or aggregate), sediment/silt traps, dewatering detention/infiltration basin, concrete washouts, stabilized construction entrances/exits, watering for dust control, seeding, mulching anderosion control blanket.

Other permanent project design features also indirectly served as BMP measures for the SWPPP and included the following: riprap outlet protection, vegetative buffer strips and preservation and protection of vegetation and trees.

Details within mandated specs required by the USBR PPP for site and construction activity were provided by SEMA including, but not limited to: nature of construction activity; intended sequence and timing of activities that disturbed the soil; total area disturbed by construction activities (including off site borrow and fill areas); location map; identifying waters of the state within one mile of the site; site maps identifying storm water flow and approximate post-grading slopes, structural and nonstructural BMPs, locations of stabilization practices, locations of off-site material, waste, borrow or equipment storage, locations of all waters of the state (including wetlands), locations where storm water discharges to a surface water and areas where final stabilization has been accomplished; and the location and description of any storm water discharge associated with industrial activity other than construction at this site.

SEMA provided a description of all pollution control measures and the general sequence during construction in which these measures were implemented as part of site and construction activity to control pollutants in storm water discharges. These measures included: silt fence slope, tracking/soil roughening, erosion control berm/diversion, check darns (hay bale, earthen, or aggregate), sediment/silt traps, concrete washouts and stabilized construction entrances/exits.

A dewatering detention/infiltration basin was designed based on site conditions and construction logistics encountered during project construction. This basin was similar to a sediment basin BMP and sized to accommodate dewatering inflows and storage, while promoting infiltration. The basin BMPs and operation were designed to provide for discharge of water satisfying permit water quality criteria.

SEMA complied with these additional control measures and requirements to further protect the environment and comply with the specifications put forth by the USBR: post-construction storm water management measures, measures to prevent the discharge of solid materials to waters of the state, measures to minimize off-site vehicle tracking sediments onto paved surfaces and the generation of dust, storage practices to minimize exposure of the materials to storm water, spill prevention control and countermeasure practices, controls for pollutant sources from areas other than construction (including storm water discharges from dedicated asphalt plants and dedicated concrete plants), controls and measures to minimize pollutant discharges, erosion and sediment control measures, provided documentation supporting determination of permit eligibility with regard to Endangered Species, complied with all applicable federal, state, or local requirements for soil and erosion control and storm water management, complied with all inspections that were conducted at least once every fourteen (14) calendar days, and within 24 hours of the end of a storm event of 0.5 inches or greater.

A completely separate spill prevention plan was developed by SEMA in the event of an oil spill at the construction site. Additionally, an arduous Asbestos Abatement Plan was developed and executed by SEMA in order to comply with USBR regulations and to further provide for environmental protection.

Throughout the course of the Red Willow Dam project, the team showed diligent focus on the protection of the environment. The SWPPP was treated as a living and evolving document from the beginning of construction to final stabilization.

What dangers and risks did you encounter, and describe any extraordinary methods used to keep workers safe?

Aforementioned, the Red Willow Dam project was completed seven months ahead of schedule, despite owner initiated change orders. This accomplishment is even more notable considering the risk and complexity of construction logistics necessitated by the owner’s unique specifications for aggregate material, and the solution that SEMA engineered in order to manage this construction material.

The project owner specified the use of aggregate material that was unavailable in the State of Nebraska. SEMA located a manufacturer in Holly, Colorado and developed a detailed transport plan to import a total of 300,000 cubic yards of this unique gravel material a distance of over 220 miles to McCook, Nebraska. This plan utilized 60 trucks every day for over six months. In order to facilitate this process and enhance the safety of the project, SEMA engineered a temporary job-specific bridge structure to facilitate aggregated hauling deliveries of gravel material to the project site.

The complexity of this plan was further impacted by the owner’s specifications that aggregate material must be conformance-tested, in-place within the embankment. SEMA had to assume all risks related to delivered material properties and quantities prior to acceptance testing.

SEMA successfully managed material deliveries based on a detailed material accounting system that relied on periodic, as-built surveys and weight-to-volume conversion evaluations. Accountable project management as well as superior supplier relationships can be credited for this.

The Red Willow Dam project experienced zero lost time injuries. A key contributor to the excellent safety record was the pre-planning that took place. SEMA developed a 54 page site-specific Safety Management Plan (SMP) for this project that outlined job-specific safety requirements, addressed potential hazards and detailed the personal protection equipment requirements. The SMP also adhered to detailed safety specifications that were outlined by the USBR.

The project team included an onsite safety manager, whose jobsite presence was required during all work hours. The safety manager was responsible for implementing safety policies and procedures; conducting safety meetings, jobsite inspections, new hire orientations, and drug testing; safety incident investigations (if necessary) and developing Job Hazard Analyses and interacts with regulatory agencies at the project location.

Daily safety briefings were conducted every morning so each crew could review the daily project goals and applicable Job Hazard Analyses. These meetings were mandatory for all onsite personnel and were conducted by the safety manager and crew supervisors. Minutes were recorded using required forms and signed by each participant.

The safety manager also conducted weekly project safety audits in order to discover and correct potential hazards, assess compliance with the Reclamation Safety and Health Standards and SEMA Safety and Health Program, assess trends and plan for new safety goals and objectives. Data from job site audits was presented during the monthly management safety meeting and corrections were required within a clearly outlined time frame. Monthly Project Safety Audits were then submitted by SEMA to the USBR.

The COR, SEMAs principal onsite representative, and designated members of respective staffs participated in scheduled monthly safety meetings. These meetings reviewed the effectiveness of SEMA’s safety effort, resolved health and safety problems relating to current operations and provided a forum for planning safe future activities. SEMA prepared and maintained meeting minutes in a manner prescribed by the COR.

The goal was to achieve and sustain an outstanding safety record through proactive risk assessments, control implementations, work practice and procedure enforcements. This goal was accomplished. Safety was never sacrificed for production on this project. The project team demonstrated a sincere commitment to protect the safety of their employees, subcontractors and the general public.

How did you leverage new technologies to work faster and reduce waste?

USBR relied upon SEMA’s experience in dam construction for best practices in sequencing and construction methodology. The specifications related to each step of the construction process were rigid in order to protect the environment as well as to protect those who relied upon Red Willow Dam for interests ranging from recreation to irrigation.

SEMA brought about innovations in technology and management applications during the embankment reconstruction phase of this project, specifically in dam excavation geotextile placement and aggregate materials management.

USBR required the use of a stipulated geonet composite on the excavated face of the dam to prevent any further leakage. This material was unique to this project and is rarely used in dam construction. The USBR specified a one-month maximum sunlight exposure limit for the geonet composite material. Innovation in construction was necessary in order to accommodate the specified exposure limitations while also constructing the embankment chimney drain in their appropriate sequence.

SEMA developed an intricate plan to manage the careful installation of the geonet material per USBRs involved specifications. An innovative process was also developed by SEMA to comply with the exposure limit for the geonet composite. SEMA built a custom-bedding box comprised of two, welded together, grain haulers. The bedding box was used to store the previously excavated (“zone-two”) material. This material would later be used to cover the geonet composite to comply with the exposure limit. SEMA also utilized a custom telescopic belt conveyor system to expedite the placement the zone-two material onto the geonet within higher zones in the dam embankment. Loaders were used to transport zone-two material from the bedding box storage to side dumps. Side dumps would dump the zone-two material into a hopper that would then feed the material onto the telescopic belt conveyor system. The mobile conveyor belt system would then place the material onto the geonet composite material on the dam face, from the bottom up. SEMA managed to limit the exposure of the geonet material to far fewer days than the specified timeframe.

This process had to be sequenced with the construction of the blanket drain as well as a 20-foot gap between the face of the dam and sand blanket, which was necessary to maximize room for the eight-foot wide chimney drain that would later be constructed.