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Ridges Basin Dam Project to Hydrate the Four Corners

Thu December 15, 2005 - West Edition
Tony Grygera

There is only one place in the United States where you can stand in four different states at the same time — at the Four Corners National Monument.

Located on the Navajo Indian Reservation where Arizona, Colorado, New Mexico and Utah meet, the Four Corners National Monument is surrounded by an abundance of mesas and buttes, rivers, trails and historical sites.

Nearby in La Plata and Montezuma Counties of southwestern Colorado and San Juan County of northwestern New Mexico, the Bureau of Reclamation is under way with the Animas-La Plata Project (ALP). The ALP fulfills requirements of the 1988 Colorado Ute Indian Water Rights Settlement Act and the Colorado Ute Settlement Act Amendment of 2000.

Initially authorized by the Colorado River Basin Project Act of 1968 and scheduled for construction in the early 1980s, the project has roots in water rights settlements dating back to 1868. The ALP’s dam, pumping plant, and reservoir facility will provide a reliable and renewable source of water for the people in the region and improve their lives.

Reclamation Commissioner John W. Keys III said, “The Animas-La Plata Project is a commitment and an investment in the future of the Four Corners Area of the United States.”

A key component of the ALP is the Ridges Basin Dam. When completed in 2008, the earthen and clay dam will have a structural height of 275 ft. and measure 1,600 ft. along its crest. It will be composed of six distinct earth material types totaling approximately 5.25 million cu. yds. of material, and will boast one of the nation’s most modern pumping plants. Together with the Lake Nighthorse reservoir, the project will provide the Four Corners area with 120,000 acre-ft. of long-term water storage. That’s one year of typical indoor water usage for approximately 420,000 households.

Storage of water in the Ridges Basin Reservoir will directly benefit seven entities:

• Southern Ute Indian Tribe,

• Ute Mountain Ute Tribe,

• Animas-La Plata Water Conservancy District,

• State of Colorado,

• Navajo Nation,

• San Juan Water Commission, and

• La Plata Conservancy District.

To put the size of the dam into perspective, its 5.25 million cu. yds. of material is approximately 1.5 times the volume of the Great Pyramid. That’s a big job but well within the capabilities of Weeminuche Construction Authority (WCA) of nearby Towaoc, CO.

The WCA is a commercial construction enterprise owned and operated by the Ute Mountain Ute Indian Tribe. Formed in 1985, WCA provides comprehensive construction services to a wide range of clients including federal, state, and local municipalities, agriculture concerns, building and heavy construction. Its management team and staff have experience in all phases of construction and related engineering disciplines.

Past projects include oil and gas field construction, residential and commercial buildings, heavy construction, road building, canals and water systems and municipal improvements. WCA does business in all the Four Corner states and qualifies as a minority business. All projects are performed with maximum use of Indian laborers and craftsmen.

Additional skilled craftsmen from the local work force complement WCA staff allowing it to handle projects over a wide range of size and scope.

Building a zoned earth-fill embankment dam is an exacting process. Proper design, faithful implementation of that design and quality materials determine whether the dam is good for the long term or destined for early failure. Of particular importance are the well-graded washed sand and aggregate materials required for construction of the dam filter blanket and chimney drain.

According to Crushing Plants Operations Manager Rob Englehart, those requirements are the reason why WCA chose process equipment from Metso Minerals and its Denver, CO-based distributor, Intermountain Construction Equipment Company.

“The plant needed high production capacity to meet the demanding project schedule, and had to produce consistent, high-quality washed aggregate and sand products that would meet stringent specifications and maintain their integrity throughout the life of the dam. Applications personnel from Metso and Intermountain worked closely with WCA and the Bureau of Reclamation in the bidding stages of the project to develop the best total solution,” Englehart said.

Indigenous material is an alluvial pit run that is intermingled with soft rock and clay. The specification for Zone 2 /2A sand filter material is very tight and demands that no natural fines be included in the product. Particular care was taken in the design of the plant to ensure that natural fines are removed, and to put into place several measures to control the sand specification curve.

These are the basic requirements:

• Remove as much minus quarter-in. natural sands and soft rock material from the feed as possible.

• Produce sand filter material from 100-percent crushed stone.

• Manufacture Zone 2/2A filter sand containing the least possible minus 200 material and with minimal particle elongation.

• Manufacture the Zone 3 washed aggregate with the least possible particle elongation and clay adhesion.

• Minimum production capacity of 350 tph of combined Zone 2 sand and Zone 3 washed aggregate.

Additional requirements of 100 tph of Zone 4-B (minus 7-in. pit run) and 152 tph of Zone-6 (7 in. by 24 in). To accomplish these levels while allowing for the waste factor required a raw feed rate of 1,150 tph.

• Stockpile the material as softly as possible to prevent degradation and segregation.

Conventional wisdom may have sought to remove clays and fines at the end of the process. That would have required an abundance of water and settling pond capacity, both of which were in short supply on the site. By removing the natural fines and soft rock at the primary stage, the waste could be hauled away in dry form and virtually all of the variations in feed — factors that cause or contribute to product inconsistency and degradation — were eliminated.

The plant was designed to allow parallel operations and features blending techniques that provide greater production and gradation efficiencies. Ease of installation and maximum portability also were important. The plant had to be up and running quickly, but would be removed from the project site after approximately two-years operation. A low profile, skid-mounted system was the answer. But two years of 24/7 duty would process more than 2 million tons of raw feed, equivalent to approximately eight years of typical aggregate plant operation.

WCA and the Bureau of Reclamation enlisted the professional assistance of Tucker and Associates Consulting Services before deciding to accept the Metso proposal.

WCA General Manager Robin Halverson, said, “The key factors in that decision included Metso’s long history of mine duty applications both in experience and equipment, Metso’s ability to design, engineer, procure and commission a plant under a turnkey agreement, and, of course, a fair price.”

How does the plant work in practice? According to Plant Superintendent Allen Higgins, “The plant was commissioned in May 2005, put into production, and met specs immediately. Since then we’ve had no difficulty in meeting specs or achieving the guaranteed capacity for the plant.”

Primary Process

The role of the primary process is to remove undesirable materials from the feed stock and to size the feed appropriate to the secondary stage.

Cat 385 excavators load 60-ton Cat 773 haul trucks, working from vertical bench faces of differing elevations, in order to separate and remove layers of clay in the pit formations and blend the various feed gradations.

Feed is hauled to the 150-ton live storage dump hopper where it is separated by a Hewitt Robins 52-in. by 24-ft. vibrating grizzly feeder with 8 ft. of grizzly deck splitting at 7 in. The oversize (7-in. by 24 in.) is stockpiled and is classified as Zone 6 material to be placed on the down stream face of the dam. The minus 7-in. material is then transferred to two Metso Svedala 8-ft. by 20-ft. scalping screens at a designed rate of 900 tph where the natural minus .25-in. component is removed. The remaining .25-in. by 7-ft. material travels to a McLannahan 8-ft. by 25-ft. dry attrition drum rotating at 16 rpm.

Material is retained in the drum for four to five minutes during which the soft and medium soft rock degrades into fines. Following the dry attrition process is another Metso Svedala 8-ft. by 20-ft. triple-deck scalping screen that removes the minus .25-in. material and also splits the .25-in. by 7-in. material into two further sizes, .25 in. by 1.5 in. and 1.5 in. by 7 in.

The .25-in. by 1.5-in. material is conveyed directly to the secondary stockpile while the 1.5-in. by 7-in. material is fed to a Metso HP400 cone crusher at 420 tph. The crusher setting is 1.1 in., and it operates in closed circuit.

Output from the HP400 crusher then goes to a Nordberg 6-ft. by 20-ft. horizontal screen separating at 1.5 in. with the oversize material recirculating back to the crusher and the minus 1.5-in. material going directly to the secondary stockpile. A 36-in. by 150-ft. radial stacker deposits the minus 1.5-in. material to a stockpile at 500 tph to be reclaimed from the two-hole surge tunnel as feed to the secondary process.

Secondary Process

The secondary process crushes and screens the material to four gradations. The minus 1.5-in. feed is extracted from the secondary stockpile and transfers to an 85-ton surge bin. Two FMC electromagnetic feeders — operating at 400 tph each — feed two BARMAC 9100 vertical shaft impact crushers operating in closed circuit. The material produced by these two BARMAC crushers is then dry screened over two Metso Svedala 8-ft. by 20-ft. screens.

The plus .75 in., .5 in. by .75 in. and .31 in. by .5 in. travel by conveyor to a dry blending facility where product can be blended for the Zone 3 wet processing plant or returned as recirculating load to the BARMAC crushers, while the minus .31-in. feeds into the tertiary process.

Tertiary Process

Material destined for Zone 2/2A feeds two Metso 7-ft. by 20-ft. horizontal wet screens. This material is split into three gradations. The plus .18 in. and .09 in. by .18 in. are conveyed to a wet blending facility which allows infinite adjustment to the final Zone 2 /2A product by addition of these fractions in controlled quantities.

The minus .09 in. is processed through individual Greystone 44-in. twin wash screws before passing through sand attrition mills supplied by Eagle Iron Works and a Greystone Twin 54-in. final washing screw. Output is then conveyed to the final Zone 2/2A product stockpile.

Material destined for Zone 3 travels from the blending facility to a Greystone Twin 44-in. Logwasher and then to a Metso 7-ft. by 20-ft. horizontal screen for a final rinse. The plus .37 in. and .14-in. by .37-in. products are then conveyed to the Zone 3 stockpile. The .09-in. by .14-in. material is stockpiled as waste while the minus .09-in. material is discarded as a slurry waste.

Zone 2/2A and Zone 3 stockpiles are constructed using Thor automated stackers, which provide soft stockpile construction without damage or degradation of the final product

All process slurry waste is pumped to a series of settling ponds via Metso 8-in. by 6-in. and 10-in. by 8-in. rubber lined pumps where decanted water is then returned to the process by 12-in. Peerless vertical turbine pumps.

For more information, call 262/717-2641.

(Tony Grygera is product marketing support manager of Metso Minerals Industries Inc.)

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