Garrison Dam Safety Modification Study

Garrison Dam Safety Modification StudyPreliminary Prime Contractor Q&ASpecial Notice W9128F23SC012BackgroundThe U.S. Army Corps of Engineers (USACE) is requesting input from prime contractors on constructability and contracting elements of the Recommended Plan for the Garrison Dam, Dam Safety Modification Study (DSMS). This is a very preliminary inquiry occurring at the latter stage of the DSMS (i.e., feasibility study phase). More detailed inquiries with the contracting community will occur as the USACE transitions into the pre-construction engineering and design (PED) phase in 2023 and beyond. Basic information regarding the project and the proposed questions that USACE has of industry are provided below.Garrison Dam is one of six USACE owned and operated mainstem dams on the Missouri River 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 1854 feet LPD, 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. 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 InformationThe 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 1,875 feet Local Project Datum (LPD). The outlet works includes an approach channel, intake structure, five power tunnels, three regulating (flood-control) tunnels, a flood tunnel stilling basin, ten surge tanks, a powerhouse, and a tailrace discharge channel.The approximately 3,000-foot-long spillway is excavated in the left abutment with a design crest elevation of 1,825 feet LPD. 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 ft at the crest to 800 ft wide in the upper half of the spillway and maintains the 800 ft width through the lower half of the chute and stilling basin. The spillway has a design discharge capacity of 827,000 cfs. The spillway underdrain system consists of a herringbone pattern of nine lateral drains connected to three longitudinal drains situated in 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. A total of six risk-driving PFMs for the spillway exist. The risk-driving PFMs are:PFM 7 – Hydraulic jacking of the spillway chute slab due to manholesPFM 7C – Hydraulic jacking of the spillway chute slab due to drain defectsPFM 8 – Hydraulic jacking of the lower spillway chute and stilling basin slab due to upliftPFM 37 – Spillway gate failurePFM 41 – Overtopping of the spillway abutment monolithsPFM 42 – Overtopping of spillway chute wallsThe Recommended Plan consists of: A full replacement of the drainage system (addresses PFMs 7 and 7C), reinforced concrete overlay in the chute and stilling basin (addresses PFMs 7, 7C, and 8), armoring the area behind the chute walls (addresses PFMs 41 and 42), raising the spillway abutment monoliths (addresses PFM 41) and constructing a deflector beam to deflect the overflow nappe from gates and modifying the gate trunnion hubs (addresses PFM 37). 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 and measures addressing the spillway gate deicing system. The total project cost of the Recommended Plan is between $500 million and $1 billion.Critical 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 during the flood season (May, June, and first half of July). Operational Constraints: The dam will be operated in accordance with the approved water control plan during the project. If during the PED any design results indicate a need to temporarily modify spillway operation for safety purposes, the water control plan shall be updated in accordance with established USACE procedures until permanent repairs are made.A substantial majority of this project is composed of the following (quantities are approximate):400,000 CY conventional concrete100,000 CY of roller compacted concrete70,000 tons of reinforcing steel600,000 CY of excavation4,700 LF of conventional concrete galleries1,600 grouted passive rock anchors (average length 90 ft each)150 post-tensioned anchors (baffle blocks and end sill) (average length 120 ft each)16,000 LF of 18-inch HDPE lateral drain with two-stage filter28 tainter gate modifications on crest structureContractor QuestionsInsights into Integrated Design and Construction (IDaC) Contracting Method1a) What is your company’s preferred contract acquisition method and would an IDaC approach have any impact on industry participation for a project of this magnitude and complexity? 1b) Given the complexities of this project and the sequencing constraints for seasonal impacts and contractor limitations, how would the USACE benefit implementing an IDaC acquisition method on this project, and do you see value in this method for this project? Contracting Structure2a) Based on the type and magnitude of work outlined above, what aspects of that work would you anticipate self-performing vs sub-contracting?2b) Would your assumptions regarding self-performance vs sub-contracting vary if the federal solicitation method were IDaC (Integrated Design and Construction)? Material Pricing Variability 3) The project’s current schedule assumption is construction beginning in 2029. Do you foresee any market changes between then and now that would substantially impact the cost or constructability of this project?Contractor Limitations / SchedulingLife safety risk to the downstream public during construction is a critical concern for the USACE. As this construction will take place in an active spillway with a small possibility of a flood requiring spillway flow, USACE’s chosen method of flood risk protection during construction is to specify contractor limitations for work that if not performed appropriately could impact the downstream public during a spillway operation event. The scope item with the most impactful contractor limitations is the replacement of the chute drains which involves demolishing lateral sections of the spillway and large excavations behind the spillway wall monoliths to construct the drainage gallery. The contractor limitations would dictate that construction is sequenced such that there is never more exposed spillway than can be closed up and the spillway made operational in the anticipated amount of flood warning time, which varies throughout the construction season. Current estimates are 10 calendar days of warning time are assumed for May, June, and the first half of July, and 30 calendar days are assumed for the second half of July, Aug, Sept, and Oct. In an emergency spillway flow scenario, the joints between new and existing concrete would need to meet specifications for water tightness (assume total applicable work includes 30,000 LF of joints and 40,000 CY of reinforced conventional concrete). In addition, backfilling behind spillway wall monoliths would be required as needed.4a) Do you have any concerns regarding the specified contractor limitations as described above?4b) The current construction contract duration estimated by USACE for this project is six years, which is significantly affected by the seasonal constraints and flood risk during construction constraints (in addition to the amount of work). In your opinion is this a reasonable amount of time to complete the project? 4c) To what degree do you anticipate these contractor limitations impacting production rates and construction sequencing efficiency?Miscellaneous5) What do you see as the biggest construction risks associated with this project and identified work activities? 6) What is your anticipated level of interest in proposing on this project in the future?7) Any additional concerns or comments you would like USACE to be aware of?InstructionsSubmission Instructions for Contractor ResponsesSubmit written responses to Lee McCormick, Contracting Officer, via e-mail at lee.m.mccormick@usace.army.mil.Written responses to contractor questions 1a) – 7) and virtual conference preferences (see following paragraph) are due May 10, 2023 by 1200 CDTInterested prime contractors may submit clarification requests to the Contracting Officer NLT 1200 CDT on May 8, 2023. USACE will endeavor consolidate and post answers to clarification requests to SAM before COB on May 9, 2023. [NOTE: Clarification requests and the USACE answers will not be confidential.]USACE acknowledges this is very short turnaround. It is understood that some responses may have little detail. It is permissible for a response to leave some questions unanswered.Only responses from interested prime construction contractors who can bond in excess of $500M will be considered.Future industry days are planned where significantly more detail and feedback will be exchanged. Feedback from interested A-E firms, subcontractors, and suppliers in addition to prime contractors will be accepted.Contractor written responses to USACE questions will not be made public. Contractors are encouraged to put protective markings on their responses.All communication should be directed to the Contracting Officer. USACE employees have been instructed not to answer questions.Virtual Conference Sessions with USACEUSACE will be conducting virtual conference sessions with interested prime construction contractors on May 15, 2023 via Webex. No other dates will be scheduled.Participation in a virtual conference session is not mandatory. Written responses from qualified prime contractors will still be accepted regardless of participation.A session will not exceed 60 minutes.USACE will not disclose any information that would give a contractor knowledge or an advantage over other interested contractors.Contractor disclosures to USACE during the conference sessions will remain confidential and will not be binding.Only contractors who submit written responses by May 10th and are assessed as qualified prime contractors will receive an invite to a virtual conference.The response submitted on May 10th should include:Whether the contractor wishes to be invited to a virtual conference sessionThe contractor’s top two time preferencesE-mail address(es) for the Webex inviteOther clarifications or questions the contractor would like to discuss with USACE during the session. [Note: USACE may decline to discuss certain topics in the interest of fairness or time.]Scheduling is based on industry response. USACE makes no commitment to select a contractor’s preferred time although it will attempt to do so. If more requests are received than can be scheduled during the day, USACE reserves the right reduce the session duration times or not invite contractors who were only minimally responsive.