Garrison Dam Spillway Modifications

***Site Visit Presentation and List of Attendees that submitted RSVPs have been added.*** VIRTUAL INDUSTRY DAY NO. 1 FOR GARRISON DAM SPILLWAY MODIFICATIONS This announcement provides details for the upcoming Virtual Industry Day. This notice does not constitute a solicitation. This announcement and the Industry Day event are intended to socialize the project to prospective contractors and for Preconstruction Engineering and Design (PED) planning purposes only. Response to this notice is strictly voluntary. The Government will not reimburse any party attending or participating for costs incurred for this event or marketing efforts. Future Industry Days are planned that will include contractor questions and one-on-one sessions with the Government. These future Industry Days will be discussed by the Government during virtual meeting No. 1. The U.S. Army Corps of Engineers, Omaha District, Virtual Industry Day event will take place from 9:00 AM to approximately 12:00 PM Central Time on September 6, 2023. The Virtual Industry Day will provide the acquisition strategy being considered, project background, project overview and construction considerations. Industry Day Attendance: The event is free of charge, and all interested parties are invited to attend. We encourage parties interested in primes, joint ventures, specificized/subcontractors, supply/vendors, and other relevant contractors to participating in this Industry Day. To receive the WebEx link for the event, each attendee must provide (1) Full Name and (2) Position and Affiliated Organization to Micah Sugiura and Nadine Catania at Micah.N.Sugiura@usace.army.mil and Nadine.L.Catania@usace.army.mil NLT August 30, 2023. Industry Questions and Comments: ALL inquiries and questions related to this Industry Day are to be submitted to Micah Sugiura and Nadine Catania at Micah.N.Sugiura@usace.army.mil and Nadine.L.Catania@usace.army.mil . Comments will be accepted via email until November 3, 2023. Background The U.S. Army Corps of Engineers (USACE) is requesting input from contractors on constructability and contracting elements of the Recommended Plan for spillway modifications from the Garrison Dam, Dam Safety Modification Study (DSMS). The DSMS was completed, and the project has officially transitioned from the feasibility study phase to the PED phase. Basic project information and critical construction constraints are provided below. Garrison Dam is one of six USACE owned and operated mainstem dams on the Missouri River mainstem system (System). It is a high hazard potential dam located in McLean and Mercer Counties, North Dakota (ND). The authorized purposes provided by Garrison Dam and the Missouri River System include flood risk management (FRM), hydroelectric power, water supply, water quality control, irrigation, recreation, navigation, and fish and wildlife. Construction was completed from the fall of 1947 through the spring of 1954. The reservoir behind Garrison Dam (Lake Sakakawea) is the largest USACE reservoir and the third largest reservoir in the U.S. When full (at the base of the Annual Flood Control and Multiple Use Zone), the reservoir is 178 miles long and up to 6 miles wide. At elevation 1855.2 feet North American Vertical Datum of 1988 (NAVD88), the top of the Exclusive Flood Control Zone, the reservoir storage capacity is 23.5 million acre-feet (MAF). This volume is almost a third of the total storage capacity of the System. A failure of either the Garrison embankment or spillway during a maximum high pool would result in widespread, long-lasting, and catastrophic consequences impacting 11 states and approximately 2,000 river miles (not including backwater areas up tributaries) extending from North Dakota to Mississippi. Garrison Dam is classified as having a Dam Safety Action Classification (DSAC) 2 (High Urgency) primarily due to the severity of incremental consequences that would occur during an uncontrolled reservoir release. Garrison Dam currently has a total of six risk-driving Potential Failure Modes (PFMs) that are associated with the spillway. As a result of these PFMs and the associated significant consequences that would result from a spillway failure, risks at the project do not meet the USACE Societal Tolerable Risk Guideline (TRG). Project Information The project consists of a zoned earthfill dam, outlet works, spillway, and reservoir. The main embankment generally runs east-west and is approximately 12,000 feet long with a maximum height of 210 feet. The dam has a crest width of 60 feet with a design crest elevation of 1,876.2 feet NAVD88. The outlet works includes an approach channel, intake structure, powerhouse with five power tunnels, three regulating (flood-control) tunnels, a flood tunnel stilling basin, and a tailrace discharge channel. The crest and spillway bridge occupy ND State Highway 200 which is a major highway through central North Dakota. The approximately 3,000-foot-long spillway is excavated in the left abutment with a design crest elevation of 1,826.2 NAVD88. The chute-type spillway structure consists of a crest structure (including Tainter gates and a bridge), paved chute channel, and a stilling basin. The chute transitions from a width of 1,336 feet at the crest to 800 feet wide in the upper half of the spillway and maintains the 800 feet width through the lower half of the chute and stilling basin. The updated Probable Maximum Flood (PMF) in 2020 resulted in decreased freeboard at the dam from 13.8 to 1.4 feet and increased spillway peak discharges from the original design discharge of 827,000 cubic feet per second (cfs) to 1,150,000 cfs. The spillway underdrain system consists of a herringbone pattern of nine lateral vitrified clay pipe drains connected to three longitudinal drains situated under the frost blanket (drainage material) beneath the reinforced concrete spillway chute slab. There are 27 manholes in the chute at the intersections of the lateral and longitudinal drains. The Recommended Plan approved in the DSMS for PED consists of: A full replacement of the spillway drainage system through selective demolition of the existing chute slab at designated new lateral drain locations, reinforced concrete overlay throughout the entire chute and stilling basin , armoring the area behind the chute walls, raising the spillway abutment monoliths, constructing a deflector beam to deflect the overflow nappe from gates, and modifying the gate trunnion hubs. Collectively, these modifications reduce the likelihood of initiation of a spillway failure and reduce risk to tolerable levels. The Recommended Plan also includes an additional line of drains on the west abutment above the powerhouse and measures addressing the spillway gate deicing system. The total project cost of the Recommended Plan is between $500 million and $1 billion A substantial majority of this project is composed of the following (quantities are preliminary, approximate, and subject to change): 400,000 cubic yards (CY) conventional reinforced concrete for new slab overlay, stilling basin modifications, and armoring behind the chute walls. 100,000 CY of mass concrete (either roller compacted concrete or CLSM/Flowable fill). 70,000 tons of reinforcing steel. Modern spillway slab joint details including 125,000 linear feet (LF) of waterstops. 600,000 CY of excavation. 16,000 LF of 18-inch high-density polyethylene (HDPE) lateral drain with two-stage filter. 4,700 LF of conventional concrete galleries. 1,600 grouted passive rock anchors (average length 90 feet each). 150 post-tensioned anchors (baffle blocks and end sill) (average length 120 feet each). 28 tainter gate modifications on crest structure. Critical Construction Constraints: Construction Work Window: The base estimate/schedule assumes construction will occur between approximately May to the end of October each year. Due to the limits on the construction season and length of construction there is risk that weather and/or flood delays could impact construction duration. Flood Risk Management During Construction: Flood water can pass through Garrison Dam via the flood control tunnels (up to approximately 100,000 cfs) or through the spillway. The bulk of the construction activities will be occurring within the spillway. Contractor exposure will be limited based on the amount of flood risk that exists. The flood season overlaps the assumed construction season in the months of May, June, and July. The spillway was only used in 2011, 2018, and 2019 in the life of the dam to discharge water as a result of high runoff events into the reservoir. The spillway was only used in 2011, 2018, and 2019 in the life of the dam to discharge water as a result of high runoff events into the reservoir. Construction Sequencing: In addition to the flood risk management during construction considerations within the spillway work area, the Contractor will have to coordinate major construction work activities in similar general working areas such as the gate control structure modification, the drainage system construction, and the concrete overlay placements. Materials availability and testing to meet project requirements: Coarse aggregate quality is a concern and a materials availability and mix design investigation in the early PED stages will be important to determine if locally sourced material is available. Coarse aggregate may need to be imported to the site from longer than anticipated distances. Concrete Delivery: Concrete delivery challenges are possible due to contractor limitations discussed above and physical site constraints such as equipment accessibility within the spillway chute and 115KV and 230 KV transmission lines interferences. The transmission lines need to be further investigated to determine the minimum acceptable clearances to determine how equipment such as cranes or pump trucks will be impacted. These impacts may dictate concrete delivery methods and concrete placement production rates. Spillway Chute Wall Excavation: Stability of the excavated cutslope behind the chute wall for construction of the gallery and drainage system features will be evaluated in the early PED phases to determine what type of slope stability support measures such as structural shotcrete and soil nail walls are required to maintain a stable and safe work area. Also, the extents of excavation may be limited by any flood risk impacts from the open excavation which would impact construction sequencing, production rates, and correspondingly the construction schedule. Dewatering: Construction work in the lower spillway chute and the stilling basin will require dewatering of about 80 feet of surrounding groundwater levels. The Government intends to perform a dewatering investigation in PED to inform the dewatering design. Dewatering systems design and construction sequencing will be critical design elements that will impact overall construction schedule and cost considerations. Tainter Gate Construction Risks: There are risks with how many gates can be taken out of service at one time for retrofits and accessibility for the proposed work. This may impact the project's ability to pass flood water and correspondingly impact construction production. Also, Contractor must ensure that the Tainter gates meet the requirements of ER 1110-2-8157 to allow personnel to work downstream of the gates. There are currently 28 stoplogs onsite that can utilized during construction for tainter gate repairs Operational Constraints: The dam will be operated in accordance with the approved water control plan during construction. Operations at the dam have not been modified as part of the study. The existing spillway that is being modified will be required to be operational for emergency flood releases if it is needed. Access/Haul Roads and Batch Plant Locations: The Government has identified locations of possible access roads, disposal areas, laydown areas, batch plant locations, etc. for Contractor consideration. Location of critical construction site features may vary between contractors depending on planned construction sequencing and construction plans by each contractor. The Government intends to get input from prospective bidders on possible construction site feature locations.