IN-DELTA STORAGE PROGRAM STAKEHOLDERS COMMITTEE MEETING URS Corporation January 22, 2003 URS Corporation January 22, 2003

2 Engineering Investigations Embankment Heights and Design Two Embankment Concepts Were Evaluated Rock toe berm on slough side Bench on slough side (variable width) Two Embankment Concepts Were Evaluated Rock toe berm on slough side Bench on slough side (variable width)

3 Rock Toe Berm Option

4 Bench Option

5 Freeboard Studies Freeboard Criterion Greater of: –3’ yr. flood stage, or –Wind wave runup + setup yr. flood stage Embankment Crest: –Webb Tract: Crest El to El 10.1 –Bacon Island: Crest El to El Crest elevation lower than for 2001 study Freeboard Criterion Greater of: –3’ yr. flood stage, or –Wind wave runup + setup yr. flood stage Embankment Crest: –Webb Tract: Crest El to El 10.1 –Bacon Island: Crest El to El Crest elevation lower than for 2001 study

6 Stability Analysis Stability analyses performed for various conditions –Rock toe berm and bench options –Various water levels in slough and reservoir –Min/max elevations of base of peat layer –Load conditions Foundation conditions for analysis from reports –Department of Water Resources –Bureau of Reclamation –Army Corps of Engineers –Consultants Stability analyses performed for various conditions –Rock toe berm and bench options –Various water levels in slough and reservoir –Min/max elevations of base of peat layer –Load conditions Foundation conditions for analysis from reports –Department of Water Resources –Bureau of Reclamation –Army Corps of Engineers –Consultants

7 Summary of Calculated Factors of Safety* LOAD CONDITION W.S. SLOUGH/RES. EMBANKMENT SIDE ROCK TOE BERM BENCH LONG-TERM -1.0 / 4.0SLOUGH LONG-TERM7.0 / emptyRESERVOIR SUDDEN DRAWDOWN 6.0 / 4.0 to emptyRESERVOIR POST-SEISMIC-1.0 / 4.0SLOUGH POST-SEISMIC3.5 / emptyRESERVOIR * Lowest F.S. shown for peat at El. –40 and –20, for rock toe berm and bench. Factors of safety for rock toe berm are greater, and seismic deformations lower, than for bench option. Risk and cost to be considered to recommend rock toe berm or bench option

8 Borrow Area Investigations Field investigation conducted in December 2002 –10 borings drilled (15’-19’ deep) totaling 165 ft on each island –Laboratory tests performed to characterize materials Borrow areas delineated – Sandy soils within 15 feet of ground surface – Volumes being estimated Results to be used for construction cost estimation Field investigation conducted in December 2002 –10 borings drilled (15’-19’ deep) totaling 165 ft on each island –Laboratory tests performed to characterize materials Borrow areas delineated – Sandy soils within 15 feet of ground surface – Volumes being estimated Results to be used for construction cost estimation

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11 Seepage Studies Seepage control alternatives considered (mostly on Webb Tract & Bacon Island) –Interceptor wells –Slurry walls –Reservoir floor clay blankets –Collector trenches Capital cost, constructibility, and operation & maintenance considerations Seepage control alternatives considered (mostly on Webb Tract & Bacon Island) –Interceptor wells –Slurry walls –Reservoir floor clay blankets –Collector trenches Capital cost, constructibility, and operation & maintenance considerations

12 Seepage Studies (cont’d) Estimated pumping rates to control seepage & exit gradients – Reservoir water el – Well 160 feet – 6 gpm to 8 gpm per well – Exit gradients less than 0.3 (criterion) Seepage control can be on Webb Tract and Bacon Island Seepage quantities are less than for 2001 study Estimated pumping rates to control seepage & exit gradients – Reservoir water el – Well 160 feet – 6 gpm to 8 gpm per well – Exit gradients less than 0.3 (criterion) Seepage control can be on Webb Tract and Bacon Island Seepage quantities are less than for 2001 study