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US water tunnel restarts amid dry spring fears

THREAT OF forest fires and Native American concerns continue to stall drives on two of three tunnels on California's Inland Feeder water project. Both the US Forest Service and the Native Americans say tunnelling had dried springs.

But British consultant Mott MacDonald said tunnelling was going well again on the 12.2km long Badlands tunnel, where work restarted at the end of last year. The firm was appointed construction managing engineer by client the Metropolitan Water District of Southern California after it had suspended work for two weeks.

The US/UK joint venture contractor Shanks Balfour Beatty tunnelling machine is averaging 70mday through weakly cemented San Timoteo Sandstone, although two zones of soft sand and silt and much harder gneiss are expected further down the route.

The fortnight delay gave MWD time to think through its strategy for the $1.2bn (£750M) feeder project, comprising a 65km long steel pipeline link between the State Water Project to the north and the new East side Reservoir east of Los Angeles, which will also be fed from the Colorado River.

The 3.5m diameter line must run through tunnel at Badlands and at two other points, Arrowhead West and Arrowhead East, also being built by Shanks Balfour Beatty.

Work started on the 9.25km Arrowhead East tunnel over a year ago but encountered heavier than expected inflow of water, threatening to dry up springs in the arid San Bernadino mountains above the alignment.

Tunnelling on the 6.5km Arrowhead West has been suspended until the other matters are resolved.

MWD said the ground was heavily fractured in this Zone Four seismic area, and while water had been expected, flows were higher than anticipated. Grouting has been under way since April 1999 and succeeded in greatly reducing inflow, MWD said. It believed the threat had passed.

The San Manuel Band of Mission Indians have a reservation south of the tunnel route but despite fears for their water, MWD said groundwater experts did not believe the springs had been impacted.

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