The Kansas City, Kan., Board of Public Utilities (BPU) recently dedicated its new $56 million Nearman Water Treatment Plant, which features what is thought to be the world's largest horizontal collector well.
The project culminates planning that began in 1991, when Black & Veatch helped the BPU develop a comprehensive master plan that showed the aging Quindaro Water Treatment Plant would be unable to meet future compliance and capacity demands. The Economic Development Administration, the Federal Emergency Management Administration, flood loss insurance proceeds and State of Kansas Community Development Block Grant all provided funding for the project.
In July and August 1993, floodwaters came within 36 inches of over-topping the river levee surrounding the Quindaro treatment plant, a 60 mgd facility. Rising groundwater undermined its oldest filtration building, removing half of BPU's rapid sand filters. Fortunately, BPU had just renovated filters in Filter Building No. 2 and they provided sufficient capacity to continue serving customers until the new plant could be built.
After first touring the plant facilities in 1995, General Manager Leon Daggett recognized that if another flood like the one that occurred in 1993 came along, 160,000 people could be without water.
"It was a real challenge to put the forces in motion to build a new plant and take away the threat to our water supply," Daggett said.
The new conventional water treatment facility provides a 36-mgd capacity with a hydraulic design capacity of 54 mgd. The plant layout will accommodate future expansion of 60 to 72 mgd. A 40-mgd, 135-feet deep, horizontal collector well, the largest alluvial well of its kind, brings raw water to the treatment plant from the aquifer.
The performance contract called for the well to produce 26 mgd, but in tests after completion, the well produced 40 mgd. Black & Veatch designed the system, and located the pump house, containing four 12-mgd pumping units, above the 500-year flood level to comply with the Economic Development Administration grant requirements.
The well has two tiers, with seven laterals per tier. The top tier is at 107 feet below grade and the other at 112 feet. The total amount of well screen installed is approximately one-half mile. The horizontal laterals vary in length from 140 to 190 feet, and consist of 12-inch internal-diameter wire wound stainless steel well screens. They are developed by purging out water to draw the fines away from the screens.
A hydraulic connection to the Missouri River replenishes the aquifer by induced recharge from the river.
"The projection is that 90 percent of the supply to the collector well is induced river infiltration," said Mike Orth, Black & Veatch Project Manager. "Ten percent is groundwater."
The overall raw water turbidity is consistently low as suspended solids are removed by passing through the riverbed. The 90/10 split of surface water to groundwater has provided a water supply with lower hardness and iron levels than vertical wells in the area. The horizontal collector well also eliminates the surface intake problems of high turbidity, Cryptosporidium, Giardia, and zebra mussels.
The new facility's treatment train consists of chlorine dioxide pre-disinfection followed by rapid mix basins. Coagulant polymer and alum are fed into the second cell to enhance particulate formation. Water flows from the rapid mix chambers into the basin influent flume. Its slotted bottom evenly distributes the flow across the basin. Three rows of horizontal paddle wheel flocculators provide three zoned and tapered flocculation stages.
Sedimentation basins provide a detention time of 4.2 hours with a surface-loading rate of 718 gpd per square foot. Two circular collectors in each basin move sediment to the hoppers at the center. Six dual-media filters consist of supporting gravel, sand and anthracite provide 4 gpm per square foot filter-loading rate with a hydraulic capacity of 8 gpm per square foot.
Three clearwells provide 15 minutes chlorine disinfectant contact time and the effluent receives ammonia treatment to form chloramine. A chlorine contact chamber can provide additional contact time if needed. A 2.6-mg reservoir provides storage where the water also is pH stabilized with sodium hydroxide and fluoridated.
The Kansas City project also included a 7,500 square foot laboratory and ancillary office space for support staff.
About 250 water industry officials, civic leaders, government officials and members of the press were on hand May 10 for the treatment plant dedication. Mayor Carol Marinovich was a featured speaker, as was the American Water Works Association (AWWA) President-Elect Robert F. Willis, Deputy Chief Engineer of the Bureau of Water Works in Portland, Ore.
