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I . OVER STORY W ATE R SUP P L r " ~ ~ . ~ < . ~ < ~ z z ffi z 3 . ~ " o > . . . o 8 ~ z Q . ~ . 8 tion," agrees Rick Kimball, project manager of the Kiewit team that built the intake. But because the rock is highly jointed in places, it complicated grouting. SNWA granted a time exten- sion. Kiewit used just two of the extra three months and earned a $I-million bonus, after starting in 1998 with a $69-million contract that ended up totalling $80 million when completed this week. The contract covered the intake, an adjoining water tunnel, well shafts imersecting the tunnel's fore bay, an aque- duct from the wells and more. With procedures similar to those used by a different can- tractor at Arizona's Roosevelt Lake (ENR 4/1/91 p. 24), Kiewit used barge-mounted clamshells, hammers and drills to gouge out a 7~ft-deep column of rock to make room for the 12-ft-dia steel intake. Divers and a remotely operated vehicle also worked in the 240-ft-deep water near Saddle Island. Less joint- ed than expected, the rock required more drilling and redrilling than anticipated. Many mere fractures lurked along the 1,60()-ft-long tunnel that ties into the intake. Tunneling under the island to create a 7-ft- radius semicircular arch and 9-ft- high walls, Kiewit crews encoun- tered faults with clay in the Precambrian gneiss. Before blasting ahead 80 ft, they drilled 100 ft ahead to grout. To control seepage for eas- ier constructibility, they tried to each even small cracks with icrofine cement that costs 10 times as much as the conventional. "1 t should have helped," Kiewit's Kim ball says. "We used twice as much grout." But starting in February 1999, Kiewit lost much of the next 40 days staunching seepage of as much as 750 gallons per minute. "We were ou tfoxed by Mother Nature," explains Stephen J. Navin, Parson 's ~ area construction manager. Rock fissures forced a big cost increase at one of North America's largest recent drilling programs, for one of the world's greatest concentrations of wells. At a mere 20x 150-ft plot on Saddle Island, 22 shafts descend 330 ft. Initial plans called for "raised boring" each f>-ft-dia shaft, by drilling a pilot hole down to the tunnel's forebay and reaming out supposed- ly solid material. Subsequent tests indicated more fractures and groundwater than suspected. Engineers considered exten- sive grouting, versus a relatively rare but more reliable and expensive lechnique-"blind boring"-with successively wider concentric drilled holes and a handling system to separate solids from water. Kiewit's team received a $7-million change order to blind bore. Since 3,000-hp turbines must fit inside the 22 holes, subcontractor Zeni Drilling Co. Morgantown, W.v., helped keep the shafts' steel casings within I~ in. of plumb. From the lake, pipelines wend across the River Mountains over grades as steep as 220. Concerned about possible flash flooding, SNWA insisted on using "controlled low-strength material" as backfill to protect buried pipes from scour. The 100-psi cement slurry costs about $22 per cu yd to make and install, compared to $13 or less for conventional granular back- fill. Forced to use the costly slurry, contractors tried not to make trenches wider than 2Jf ft. Blasting makes the trenches too wide, notes Bill Bevilacqua, project superintendent at Las Vegas-based Contri Construction Co., whose crews switched to rock saws before laying 3 miles of 9-ft-dia pipe for $15 million. NEW PLANT The mountains also made the siting difficult for a new plant. The II-acre Smith site, wedged in the Lake Mead National Recreation Area, seemed too small. Turning to the Las Vegas Valley, SNWA repeatedly ran into plans for new sub- divisions, before settling on an alluvial fan within }j mile of homes in Henderson. With memories of industrial accidents nearby, neighbors worried about chlorine gas wafting down the hill, so Montgomery Watson/CH2M Hill designed the new Riv- er Mountains plant to use less dangerous liquid chlorine. Using ordinary salt, a record-sized, on.site facility will produce sodium hypochlorite to make the chlorine. "It's innovative and almost unheard of in treatment plants of this magnitude," says MW" Project Manager Charles O. Bromley. The plant's contro- versial plan calls for an initial capacity of 150 mgd plus construction of shells for a later 150-mgd expansion. With seven cranes and 30 major stmctures under constmction on just 15% of the 415-acre-site, Kiewit received the $31-million change order in February to build shells for eventual filters, flocculation, ozone contactors and equal- ization basins. The change saves $7 million in soft COSlS, keeps others from getting in the way and forcing delay claims, and min- imizes future disruptions of neighbors, SNWA officials say. And given Kiewit's command of the site, it made no sense to advertise a "phony bid," Mulroy says. Some critics say the entire plan makes no sense; to use the second 150-mgd shells, SNWA needs more water. Besides bank- ing river water now and lobbying for permission to use current river surpluses, SNWA proposes "taking" flows from Colorado River tributaries in Nevada but wheeling the water through the river-a plan opposed by the Los Angeles-based Metropolitan Water District of Southern California and others. But even MWD's expert on Colorado River matters, former U.S. Bureau of Reclamation Commissioner Dennis B. Underwood, com- mends Mulroy as a "dynamic" leader with "a lot of initiative." Mulroy, 47, and a self-described "big mouth," once dreamt of working as an overseas diplomat, then quit a Stanford Uni- versity doctoral program in German literature. Now as she takes a gamble, she hopes to convince Colorado River interests to buoy the Las Vegas Valley's continuing growth. By David B. Rosenbanm in Las Vegas GAMBLER Las Vegas Valley water czar Patri- cia Mulroy, dedi- cating the new lake Mead intake, seeks a relaxation of Colorado River rules. The gam- bling mecca's population in- creased 64% in the last decade. ~ . S t " o 5 Ii 66 ENR/ APRtt. 24, 2000