Seattle Future Sources

Aside from the Tacoma-Seattle Intertie, which is detailed in the Tacoma Workbook, Seattle is evaluating other alternatives for increasing its water supply. The sources listed in Table 8.5 have been incorporated into the CRYSTAL model and can be evaluated for performance relative to the Second Supply Project.

Source	Comments
Drawdown in South Fork Tolt Reservoir	South Fork Tolt Reservoir drawdown levels can be increased when the Tolt Treatment Facility is brought online to address turbidity issues. In addition, incorporating the Tolt Treatment Facility will change dead storage elevation in the South Fork Tolt Reservoir from 1730’ to 1710’. This option is estimated to provide an additional 11 mgd in yield (Seattle, 1999). This action is connected to different instream flow requirements that have been incorporated into CRYSTAL.
Additional Drawdown in South Fork Tolt Reservoir	After the implementation of the Tolt Treatment Facility, Further drawdown of the reservoir to 1690' or 1660' is possible. Seattle estimates an additional increase yield of 8 mgd (for a total benefit of 19 mgd for the Tolt Treatment Facility) (Seattle, 1999).
Highline Aquifer Storage and Recharge	The Highline wells are used during summer peaking periods, at a current capacity of 10 mgd. Aquifer storage and recharge studies suggest that a yield of 12-15 mgd could be provided for up to 4 months.

The sources listed in Table 8.6 include some of the regional supply options that are currently being evaluated by Seattle. These elements have not yet been incorporated into the CRYSTAL model.

Source	Comments
Additional Drawdown in Chester Morse Reservoir	Pumping of water in Chester Morse Lake below the natural outlet helped mitigate potential shortfalls in 1987. This option may be incorporated into permanent operation policies as reliable supply. Current discussions with fisheries managers on the Cedar River suggest that this option may be implemented only once in every 4 years, and would be dependent on the outcome of instream flow negotiations. Yield from this potential supply is estimated at 20 mgd (Seattle, 1999).
Diversion on the North Fork Tolt	A diversion intake would be constructed on the North Fork Tolt River, and would be operated in conjunction with the existing South Fork Tolt facilities. This water would be diverted into transmission pipelines for supply during winter, allowing the Tolt Reservoir to refill. During summer, water stored in the Tolt Reservoir would be used to meet municipal demands and instream fish flows until the North Fork flows exceeded the instream flow requirements. Yield from this potential supply is estimated at 40 mgd (Seattle, 1999).
Development of the Snoqualmie Aquifer	In 1994, the East King County Regional Water Association (EKCRWA) and Seattle filed a joint water right application to withdraw 60 mgd from the Upper Snoqualmie basin. Groundwater would be extracted to augment streamflows and to meet municipal demands. Technical studies conducted to support the water right application indicate that this supply may provide up to 16 mgd in additional yield (Seattle, 1999).

8.2.7 Seattle Future Sources