Description
*AWARDED* 1.1. Description of Services / Introduction: The sub-surface drainage system is an integral component of the spillway structure at Oahe Dam. Cleaning of this system and the visual inspection of the drains and collector pipes with remote-operated camera equipment is required to document the existing condition of the system. The Contractor shall provide all personnel, equipment, supplies, facilities, transportation, tools, materials, supervision, and other items and services necessary to clean and to inspect the spillway sub-drains and collector pipes as defined in this Performance Work Statement, except for those items specified as government furnished property and services. The Contractor shall perform to the standards in this Contract. 1.2. General Project and Spillway Structure Information: 1.2.1. Project Information: The Oahe Dam and Lake Project is a federally owned facility. Oahe Dam is located in Hughes and Stanley Counties in central South Dakota on the Missouri River, approximately 6 miles upstream of the city of Pierre and approximately 1,072 river miles upstream of the mouth of the river. Oahe is the third dam (downstream) of a system of six mainstem Omaha District dams on the Missouri River. Vicinity and location maps for the Project are shown on Sheet C-001. The general location of the spillway with relation to local highways along with Contractor access routes is also provided on Sheet C-001. 1.2.2. Spillway Structure and Channel Information. The spillway for Oahe Dam is located in a narrow valley in the far right abutment of the dam, approximately one mile from the northwest end of the embankment as shown in Sheet C-001. The spillway consists of an unlined approach channel, a gated spillway structure, and a discharge channel. The use of the spillway was designed to be a rare occurrence. Since completion, the spillway has not been used for release of water. Small volumes of water have been released through the spillway during periodic exercising of spillway tainter gates and for other maintenance related reasons. The spillway gate structure consists of an eight bay, flat-crested weir; a depressed stilling basin; and a downstream apron as shown on the general layout Sheet C-100. The weir crest and apron slab were constructed at elevation 1596.5 feet and the depressed stilling basin was constructed at elevation 1590.0 feet. The spillway weir is comprised of seven monoliths and two end segments built integrally with each abutment. The weir has an overall length of 456 feet from abutment face to abutment face. Each monolith consists of an 8-foot wide center pier and 25 feet of weir on each side of the pier. The piers support the tainter gates, bridge, gate hoist machinery and auxiliary equipment. Eight tainter gates, each 50 feet wide by 23.5 feet high, are located between the piers. In a closed position, top of tainter gate elevation is 1620.0 feet. Each gate was retrofitted with a 1-foot high inclined splash plate to elevation 1621.0 feet. Non-overflow abutments on each side of the weir house auxiliary equipment and contain drainage galleries that collect water from the weir, backfill, and frost blanket drainage system. The depressed basin of the spillway extends downstream from the weir approximately 100 feet to the end sill. The end sill is a gravity concrete block structure that is anchored to the shale foundation by reinforcing bars grouted into drilled holes. The apron slab extends approximately 209 feet downstream from the end sill. Both the depressed basin and apron slab are 18 inches thick and were constructed over a 5’-4” thick frost blanket layer and anchored to the shale foundation with reinforcing bars grouted 10 feet below the bottom of the frost blanket. The frost blanket together with the apron slab, serve to protect the foundation from frost action and facilitates drainage beneath the slab. A discharge channel extends approximately two miles downstream from the spillway gate structure. Immediately downstream of the spillway structure cutoff wall, the channel bottom narrows to an approximate width of 334 feet and then remains constant. Between the cutoff wall and 140 feet downstream of the cutoff, the channel side slopes transition from 1V on 2.5H to 1V on 3H. The side slopes are armored with riprap in the transition area and the channel bottom is armored with riprap for 240 feet downstream of the cutoff wall. The remainder of the downstream channel is comprised of unprotected shale surfaces. The channel is straight except for one bend located approximately one-half of the distance to the downstream end of the channel. The downstream end of the channel directs flows into a valley allowing discharges to flow across the flood plain toward the river channel. 1.2.3. Spillway Structure Drainage System. An extensive system of drainage and collector pipes and foundation drains (over 8,400 feet) exist beneath the spillway weir; in the abutment galleries; beneath the stilling basin and apron slabs; behind the walls; and behind the apron blocks. The pipes range in diameter from 6 to 12 inches. Pipe material types include perforated vitrified clay pipe (VCP), solid cement asbestos pipe (CAP), solid cast iron pipe (CIP), perforated and solid plastic pipe (PP), perforated and solid galvanized standard steel pipe (GP) and solid corrugated metal pipe (CMP). 1.3 Objectives: The overall objective of this Contract is to clean and thoroughly document the existing condition of the sub-surface drains and collector pipes of the spillway structure. 1.4 Scope: The scope of work for this Contract generally consists of (1) cleaning the spillway structure drainage system pipes and drains by hydro-flushing them (flushing them with large quantities of water or jetting them), (2) visually inspecting the pipes with remote-operated camera equipment and (3) producing a detailed formal report that thoroughly documents the condition of these features. Deliverables for this work will include DVD(s) of the inspection footage and a report that summarizes the procedures and findings of all inspections and includes individual inspection logs that summarizes the condition each pipe segment and documents the location of any significant observation. The Contractor shall perform these services as noted in this PWS. All work shall be conducted in accordance with current professional standards, Corps of Engineers policies, regulations, and procedures. The Contractor is responsible for supplying all equipment, supplies, materials, and personnel necessary for the completion of this work. 1.5 Scope Period of Performance: The period of performance for the PWS shall be 180 days from the date of Notice to Proceed (NTP). Upon receipt of NTP, the Contractor shall submit a draft baseline schedule for completion of the tasks in this PWS for approval to meet the milestones as indicated below. The baseline schedule shall be based on calendar days and shall include milestones for completion of each task provided herein.