DEVIL’S SLIDE TUNNELS

Client: KIEWIT

Location: Pacifica, CA

About the Project

Devil’s Slide Tunnels were designed by California Department of Transportation (Caltrans) to re-route existing Highway 1 traffic around an unstable geologic formation called Devil’s Slide.  Two 28′ diameter tunnels approximately 1 mile long with 10 cross passages were constructed.  During excavation, groundwater and process drilling water was expected to reach a maximum of 650 gpm.  Treated groundwater was discharged directly to the Pacific Ocean under an individual NPDES permit.  A separate 650 gpm stormwater system was also set up for discharge.

Treatment

The non-storm water treatment was originally designed for pH, turbidity, and hydrocarbons.  Treatment components included pretreatment open top weir tanks, modular panel style treatment tanks, a control module (water quality monitoring-reporting), chemical injections system, bag and cartridge filter system, and hydrocarbon removal system. Limits for pH were 6.5 to 8.5 S.U. with continuous monitoring. Turbidity limit was <50 NTU’s instantaneous maximum. During annual testing, Chromium VI was detected above the Basin Plan, which necessitated a project shut down.  Clear Creek solved this problem overnight by reducing it to Chromium III through an on-site treatment, putting the project back on schedule for our client.  A similar 650 gpm system was set up for storm water discharges using a lined earthen basin.  Clear Creek provided 24 hour monitoring and operations on-site.

Market:

Construction

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