Figure 216. --Ironworkers riding the carriage as radio. All movement of the tailtowers, carriage travel, and hoisting was from these remote control stations. It should be noted that an elevation differential of 180 feet existed between the connections of the main line at the stationary headtower and the traveling tailtowers, creating a steep slope at the headtower side. Both cableways were used to place concrete during the heaviest placing schedule, but usually one was used for concrete work and one for yarding. The conveying lines had a carriage travel speed of 1, 200 feet per minute and the hoist lines a speed of 400 feet per minute. The rated capacity of the main cable was 25 tons with a tension breaking strength of 580 tons. The cableway units were unique in that the hoist line was reaved from the hoist drum through the carriage and dead-ended on the tailtowers. This permitted moving the carriage along the span and maintaining the load at a given elevation, allowing independent movement for hoisting or conveying. Total horsepower requirement for two cableways was 1, 840. 248. Contractor's Major Mobile Equipment. The contractor's construction and yard equipment consisted of the following: 1/Where the type and size or capacity of a particular make and model of equipment were not stated in the original report, these have been obtained from current construction equipment catalogs. As specifications for a particular model may vary from year to year, some minor discrepancies may exist between the reported size or capacity and that of the equipment actually used. 249. Water Supply System. The specifications required the contractor to furnish 120,000 gallons of potable water daily to the Government water distribution system for Government community use in addition to all the water required for his camps and work areas. To supply the required quantity, the contractor pumped water from an infiltration gallery located about one-fourth mile below the damsite. Two 300-g.p.m., 1, 500-foot-head, electrically powered pumps pumped the water through a 6-inch supply line buried 6 feet in the ground to the water treatment plant. The water treatment plant, located about 3,000 feet from the Government distribution main, consisted of a "packaged" unit furnished by the International Filtration Co. The unit included facilities for chemical mixing, coagulation and sedimentation, rapid sand filtration, and chlorination. In addition to the packaged unit, the treatment plant had additional sedimentation provided by a 60, 000-gallon retention tank located outside the treatment plant and placed to function between the coagulating tank and the rapid sand filters. The total settling period of the treatment plant was about 4 hours with the plant operating at 200 gallons per minute. Each of the two rapid sand filters had a capacity of 100 gallons per minute at rates of 2 gallons per square foot per minute. From the clear well at the treatment plant, the water flowed through an 8-inch main to a 300, 000-gallon insulated supply tank. From this tank the water then flowed by gravity through an 8-inch main to a junction with the Government camp distribution system. Static pressures in the Government camp were maintained between a maximum of about 125 pounds per square inch at the low end of camp to a minimum of about 60 pounds per square inch at the higher elevations in the camp. The water treatment plant was placed in service supplying water to the Government camp on June 22, 1959. The plant was operated on a 24-hour-day basis for most of the summer with an operating staff of one operator, assisted occasionally by one man. In operating the plant the contractor was limited by the Utah State Department of Health to a rate of 200 gallons per minute except for short periods during peak demand when the maximum pump capacity of 300 gallons per minute was allowed. The turbidity of the raw water in 1959 ranged from a low of 40 parts per million registered in July to a high of 12,500 parts per million registered in September. This great range in turbidity occurred at times within a very few hours. The rapid turbidity fluctuation resulted in an upset of the chemical flocculent and a marked decrease in the efficiency of coagulation. Because of this rapid change in turbidity it was apparent that the 4-hour sedimentation time was very necessary and the plant could not provide a water that would consistently meet State drinking water standards if the plant capacity was increased to 300 gallons per minute without adding additional retention capacity to obtain an increased sedimentation period. To improve the quality of water during peak demand, the contractor dozed out an open retention pond at the water treatment plant and presettled the raw water before it entered the water treatment plant. During the winter months when the plant was normally operated only one shift out of three, the contractor drained the water supply line from the water treatment plant to the river pumping station each time the plant was shut down. This procedure was standard practice with the plant operators who were concerned that one section of exposed, insulated, electrically heated pipe located between the river pumping station and the beginning of the 6-foot ditch might freeze if a power failure occurred during an extremely cold period. Within a few months after placing the river pumping station in operation in June 1959, the water delivery pressure at the water treatment plant began decreasing. The drop in pressure was due to silt gradually plugging the infiltration pipes and continued until it became impossible to deliver the required quantity of water. The contractor valved the piping system at each pump so the pumps could be individually back flushed, and by occasionally back flushing, the difficulty was partially alleviated. As water demands increased during the spring of 1960, the infiltration pipes plugged more solidly and back flushing was required more frequently. The difficulties of operation finally culminated with several pump failures and one pump motor burning out. These failures occurred in June and July of 1960. In August 1960, the contractor made a temporary connection between the "construction" water supply tanks located on the dam left abutment and the domestic water force main and began supplying water from this source. The infiltration pipe main was uncovered and water was back flushed through the system. Waterflows indicated there was only one point of supply, which was located at about the point of intersection of the main with the first lateral infiltration pipe along the streambank. The infiltration main seemed to be plugged solidly with silt except for a small passage along the crown segment of the pipe. The contractor removed the infiltration main and dredged an open channel from the pump structure to the river channel. All backfill was removed from beneath the pump structure to about elevation 5592.8 and the structure was enclosed with 2- by 12-inch planks and corrugated metal siding. The pump intake lines were wrapped with heat tapes and electric heaters were installed within the enclosure. During the summer of 1960 water samples were taken upstream of the water pumping plant and compared to water samples taken at the water treatment plant. There was never any significant difference in the amount of suspended solids in water samples taken on the same day indicating that the filtering action of the infiltration bed was negligible. After making the revisions to the water supply intake system the contractor experienced no further major difficulty. The Dutch John water supply system was operated by the contractor during the remainder of the contract and efforts were continued to make the plant operate automatically, but generally more automation resulted in decreased quality of plant operation. Operating personnel consisted of one operator and an assistant, both working part time. The contract requirement for 120, 000 gallons of water a day to the Government camp was inadequate during the summer months and consequently camp lawn watering had to be regulated. For example, about 40, 000 gallons a day were adequate in the winter but on July 19, 1961, the Government camp used 359, 000 gallons of water in 24 hours. 250. Sewage Treatment Plant. Sewage from the Dutch John community flows by gravity to a sewage treatment plant where it is processed through an Imhoff tank, a trickling filter, and then to a final settling tank. In the settling tank an adjustable portion of the influent can be pumped back to the Imhoff dosing tank and then be recirculated through the trickling filter. From the final settlement tank the influent flows by gravity to two stabilization ponds connected in series. The operation of the sewage treatment plant presented no difficulties except that with the beginning of 0° F. weather in the winter it was always necessary, because of the danger of freezing the sprinkler piping, to bypass the trickling filter and deliver the plant influent directly from the Imhoff tank to the stabilization ponds. The plant was maintained by Arch Dam Constructors. One man spent an average of about 2 hours a day cleaning the treatment plant, removing debris from screens, withdrawing sludge to the sludge drying bed, and other routine maintenance duties. The two stabilization ponds had about twice the capacity needed, since the upper pond very seldom overflowed and then the overflow formed only a very small puddle in the lower pond. During summer months when the sewage load was greatest, evaporation loss was also at its greatest and the upper pond did not overflow. CHAPTER XIV. Construction --COMPLETION OF DAM, POWERPLANT, APPURTENANT STRUCTURES, AND INSTALLATION OF GENERATING EQUIPMENT A. Principal Work Under Specifications No. DC-5700 1. Switchyard Earthwork 251. General. Gunther and Shirley Co. and E. V. Lane Corp., prime contractors for completion of Flaming Gorge Powerplant and Switchyard received notice to proceed on part (1) of the schedule (switchyard earthwork) and extension on February 26, 1962 (sec. 142). Switchyard earthwork and excavation for concrete structures, backfill, gravel surfacing, and soil sterilant in part (4) of schedule were subcontracted to Stan Robins Construction Co. of Vernal, Utah. The subcontractor moved in equipment and started work in April 1962. 252. Clearing. A 191-horsepower bulldozer was used to uproot and pile the small number of trees that were cleared in the extension of the switchyard and access road. Clearing for transmission tower footing sites was done by hand labor using chain saws. Burning was done at various times in accordance with Forest Service regulations. The right-of-way for connecting transmission lines to the switchyard was cleared and burned in June 1963 by Government forces. 253. Excavation. The subcontractor started excavation on the switchyard extension in April 1962 and substantially completed this work by the first of July 1962. Some blasting of rock was necessary in the ditches. A 191-horsepower bulldozer and scraper did the rough excavation and hauled the material into the designated waste area. A 3/4-cubic-yard backhoe was used to excavate the ditches. A 115-horsepower motor grader was used to bring the area to subgrade. Structure excavation and other switchyard earthwork were started in May 1962 and were substantially complete by July 1963. Some footing modification and blasting became necessary in switchyard structures because of rock. A 250-c.f.m. air compressor and a jackhammer were used to drill shot holes and anchor bar holes. Material was excavated by the backhoe. Hand labor was used to bring the subgrade to final grade. Material was stockpiled for backfill or hauled to the waste area by a rubbertired tractor shovel loader. Blasting was necessary on the control tunnel and outlet structure, as all excavation was in rock. Excavation of the footing on the transformer circuit tower C1-T1 was done by hand labor because it was inaccessible to power equipment. A 300-foot-long wooden ramp had to be constructed, and muck was hauled over the ramp in concrete buggies pulled by an electric winch. The muck was dumped into a waste area 300 feet downstream of the tower site. The prime contractor started excavation on the 138/230-kilovolt addition to the switchyard in May 1963 and substantially completed this work by July 1963. 254. Backfill. The subcontractor commenced placing backfill in October 1962 and substantially completed the operation by September 1963. The prime contractor backfilled around the foundations in the 138/230-kilovolt addition during July and August of 1963. Excavated material was stockpiled and later used for backfill. During excavation and subsequent handling the tertiary sandstone broke down to the individual grain size and physically resembled the soil mantle in the switchyard area. The typical backfill material had a unified soil classification of SP-SM.1/ A typical sample of the soil had the gradation shown below. About 11 percent of the entire sample was retained on the No. 4 screen, and the gradation of the portion passing the No. 4 screen is shown below as the percentage retained on each screen size. 17"Earth Manual, Bureau of Reclamation, first edition, 1960. |