Water Supply Planning

Cascade Ensures Water Reliability

The mission of Cascade Water Alliance is to provide water supply of the highest water quality standards to meet current and future needs of members in a cost effective, environmentally responsible manner. Cascade ensures water reliability; our members are the source of water quality.

Water Supply Portfolio

For most of the past decade, conservation programs (including changes to plumbing codes), utility efficiency efforts, lifestyle changes and development patterns have contributed to greatly slowing the increase in water demand. Based on recent trends, the Cascade TSP forecasts the demand for water in Cascade’s service area will remain relatively unchanged through approximately 2020.

For the Cascade TSP, Cascade evaluated a wide range of water supply options to meet long-term needs. These included additional or expanded contracted supplies from existing sources within the Central Puget Sound region; new surface water supplies, new ground water supplies, reclaimed water and enhanced water conservation. From an initial list of 27 possible sources, a preferred supply “portfolio” was selected that includes the following sources:

  • Continued production from member supplies serving their respective service areas.
  • Continued use of water from SPU under the Block Contract.
  • Beginning in 2024, delivery of water from TPU and Covington Water District, which requires construction of additional transmission pipelines.
  • Beginning in 2030 (or as needed) water from Cascade’s White River – Lake Tapps Reservoir Project, which requires construction of a treatment facility and additional transmission pipelines.

Under the preferred portfolio, available supplies are expected to exceed Cascade’s forecast water demand throughout the 50-year planning period.

Cascade’s supply planning principles call for maintaining a high degree of flexibility to match available supplies with water needs as economically as possible.

Cascade plans to develop the necessary water treatment and delivery infrastructure in phases over time. While Lake Tapps provides a critical resource for the long term, Cascade will seek opportunities to delay construction of both phases in order to spread the costs of infrastructure development over a longer period of time.

During development of the Cascade TSP, discussions were underway with both SPU and TPU regarding possible changes in the quantity and terms for supply available to Cascade. Changes to Cascade’s wholesale contracts with SPU and TPU have been successfully negotiated. The newly structured contracts do not change the preferred supply portfolio through 2024.

The result of these contract modifications is that Cascade will be able to meet the projected 2040 demands of its members utilizing Member Independent Supply and purchased water. After 2040, Lake Tapps will allow Cascade to meet projected demands beyond 2060. (The portfolios below reflect the modified SPU and TPU contracts and Covington Water District withdrawal from Cascade).

Cascade Supply Portfolio (Average Day)
Cascade Supply Portfolio (Maximum Week)

Water Supply Portfolio

Cascade has developed a long-term Capital Improvement Plan (CIP) for development of the supply portfolio. Major projects include construction of the Tacoma-Cascade Pipeline by 2024 and construction of the Lake Tapps Project in two phases at 2030 and 2045. The estimated cost of the projects described in the 50 Year CIP is approximately $950 million.

Recent changes in Cascade’s wholesale purchase contracts with SPU and TPU will likely delay when these projects are actually needed. Cascade will continue to monitor member demand and adjust the anticipated construction schedule for needed infrastructure.

Anticipated sources of funding for infrastructure construction include revenue bonds and capital reserves, including income from Cascade’s Regional Capital Facilities Charges (RCFCs) collected from members over time. Cascade will also seek lower-cost sources of funding, such as grants and loans from state and federal sources.

Water Supply Outlook

Updated July 18, 2013

During the month of June, Cascade used 30.9 million gallons of water per day from the Seattle system. This represents a usage of 117% compared to the same period in 2012.

Climate Outlook

Long range climate outlook for the Puget Sound Region from the National Weather Service Climate Prediction Center, as of July 18, 2013.

30-Day Climate Outlook:

The Puget Sound Region Climate Outlook for the next thirty days indicates a probability of above average temperatures and average precipitation.

90-Day Climate Outlook:

The Puget Sound Region Climate Outlook for the next ninety days indicates a probability of above average temperatures and average precipitation.

Wholesale Water Purchase

Cascade currently utilizes a combination of member groundwater supplies and regional supplies purchased on a wholesale basis to meet the water needs of its members. Cascade has entered into long-term wholesale water purchase contracts with Seattle Public Utilities (SPU) and Tacoma Public Utilities (TPU). This combination of supply sources enables Cascade to meet the forecast water demands of its members through 2040.

Seattle Public Utilities Agreement

In 2003, Cascade entered into a “block” contract with SPU for the sale and purchase of potable water.  In 2013, Cascade and SPU amended this contract to provide for a block supply of 33.3 MGD (average annual day) through 2039 (through a combination of the original block and varying amounts of supplemental supply).  After that date, the available block declines by one MGD annually until 2064, when 5.3 MGD will remain available from SPU through 2075.  The amended contract will be reviewed and can be modified.

The original “block” contract between Cascade and SPU (signed in 2003) obligated SPU to provide potable water (and obligated Cascade to purchase it) through 2053.  The quantity through 2023 was 30.3 MGD on an average annual day (additional water is provided during the Peak Season and Peak Month).  The amount of water available then declined in 5 MGD increments every five years, beginning in 2024.  For the last 10 years of the agreement, Cascade would receive 5.3 MGD.

In late 2008, Cascade and SPU approved amendments to the block contract effective January 1, 2009.  Under that amended Agreement, the Cascade Block would be increased by 3 million gallons per day (MGD) from 2009 to 2017 and 5 MGD from 2018 to 2023 (for a total block of 33.3 and 35.3 MGD respectively).  This supplemental supply was provided at a different rate from the base block.

Tacoma Public Utilities Contract

In October 2005, Cascade and TPU executed an Agreement for the Sale of Wholesale water. Water purchased by Cascade would help fulfill Cascade’s supply needs beginning in 2008.

In 2012, Cascade and TPU agreed to amend the wholesale water purchase agreement.  Under the amended agreement, Cascade would make specified supply capacity reservation payments to TPU, in lieu of the minimum purchase payments provided for in the 2005 agreement.  TPU agreed to provide up to 8 MGD of supply to Cascade through 2042.  The amended agreement also provides for Tacoma to sell water supply directly to certain municipalities in connection with the reallocated capital payments that creates an additional means (i.e., substitute water supply) of satisfying Cascade’s obligations to such municipalities arising out of the 2010 agreement between Cascade and the Cities of Auburn, Bonney Lake, Buckley and Sumner.