Design and Construction of a 200-foot-deep, 24-foot-diameter Conveyance System Access Shaft

Boise, Idaho September 14, 2009 Design and Construction of a 200-foot-deep, 24-foot-diameter Conveyance System Access Shaft Placeholder for photo Daniel R. Williams, P.E.

Project Overview 2

Project Location Map Treatment Plant Effluent Conveyance System Brightwater WWTP 36 MGD in 2010; Peak Flow 130 MGD 54 MGD in 2040; Peak Flow 170 MGD Membrane bio-reactor WWTP Reclaimed water facilities Conveyance Tunnels Length (feet) East 13,890 18 Central 19,020 11,590 Outside Diameter 17 17 West 21,033 13 Seattle Bellevue 3

Ballinger Way Portal Design Phase PREDESIGN REPORT: Describes a BWP large enough to serve as a retrieval shaft for two TBMs Location based maximum tunnel length and depth based on hydraulics Tunnel BT3 is 3.8 miles in length Tunnel BT4 is 3.9 miles in length Anticipates an inside diameter of 30 feet 4

Brightwater Effluent System PLAN PROFILE

Ballinger Way Portal Design Phase TECHNICAL MEMORANDUMS: Tunnel and Portal Access TM Describes inspection intervals and access requirements for Brightwater System Inspection and maintenance at BWP by remote operated vehicles (10 x 10 ) Technical Advisory Committee Report Proposes a drilled shaft 10 feet in diameter 6

Ballinger Way Portal Design Phase TASK: Evaluate consequences of reducing the inside diameter of the BWP from 30 feet to 10 feet.

Ballinger Way Portal Design Phase Why reduce the diameter? Large diameter BWP could take 15 months to construct at a cost of $13M. Drilled shaft BWP could be constructed in several months for a cost of $1.5M. Problems? Complex tunnel-to-portal and tunnel-to-tunnel connections (Drilled shaft not large to receive TBMs). 8

Ballinger Way Portal Design Phase Soil Conditions at BWP / Tunnel Interface: Flowing or unstable soil from scattered sand, silty sand, and silty gravel layers; hydrostatic head of 150 feet at base of BWP Inspection / Maintenance Requirements: Initial inspection after ten years of operation After 7.0 or larger quake 30-year intervals Submersible and crawler-type ROVs 9

Ballinger Way Portal Design Phase ALTERNATIVES: #1 Small Diameter Portal (i.e., Drilled Shaft) 1a Portal above Tunnel Intersection 1b Portal West of Tunnel Intersection 1c Portal East of Tunnel Intersection #2 Large Diameter Portal 10

Ballinger Way Portal Design Phase Constructability and Risk (Drilled Shaft Alternative): Unstable flowing soil conditions where tunnel-to-tunnel and tunnel-to-portal connections occur. Groundwater pressure at connections is 60-plus psi. Requires grouting (in absence of dewatering) to safely conduct hand-mined excavations. Effectiveness of grouting is difficult to verify; incomplete grouting could compromise hand-mined excavations, exposing workers and the tunnels to soil and groundwater. Increases the likelihood of Contractor claims and schedule delays. 13

Ballinger Way Portal Design Phase Schedule Impacts (Drilled Shaft Alternative): Drilled shaft cannot be constructed independently of tunnels (so drilled shaft is on the critical path). Cost (Drilled Shaft Alternative): Estimated cost of drilled shaft alternative is $7.2M. Large diameter portal alternative costs ranged from $6M to $14M. 14

Ballinger Way Portal Design Phase ALTERNATIVE #2 Large Diameter Portal 15

Ballinger Way Portal Design Phase TASK: Evaluate the following four alternative excavation support systems: Sequential Excavation w/ Depressurization Open Caisson Ground Freeze Wall Slurry Diaphragm Wall 16

Ballinger Way Portal Design Phase Alt 2a Sequential Excavation with Depressurization Alternative was ruled out because of concerns about volume of groundwater removal and ability of Contractor to keep shaft dewatered. 17

Ballinger Way Portal Design Phase Alt 2b Open Caisson Alternative was ruled out because of concerns about plumbness and keeping caisson moving downward at the depths required. 18

Ballinger Way Portal Design Phase Alt 2c Ground Freeze Wall Alternative was allowed because of past success on other projects similar in size and scope represented best chance for success. 19

Ballinger Way Portal Design Phase Alt 2d Slurry Diaphragm Wall Alternative was allowed because of past success on other projects similar in size and scope represented best chance for success. 20

Ballinger Way Portal Design Phase Alternative Costs: 1. Sequential Excavation w/depressurization -- $8.19M 2. Ground Freeze Wall -- $14.56M 3. Slurry Diaphragm Wall -- $9.17M 4. Caisson -- $6.3M 21

Ballinger Way Portal Design Phase Reclaimed Water Pipeline Pipe Support Design 20-inch diameter pipe, 170-foot-tall column Thermal expansion when temp rises from 40-deg to 90-deg = 0.65 inches Force imparted by pinned pipe = 165,000 lbs Therefore, pipe supports designed to allow for thermal expansion Polymer material is placed between the steel strap and the pipe itself, which allows the pipe to move vertically within the pipe support. Polymer material is used for skids on casing spacers and is used on boat docks. 22

Ballinger Way Portal Construction Phase 23