Central Sammamish out of sewage capacity; County dumps on development

King County removed a critical sewage line project from its plans. Current system is too small for future development north of SE 8th St.

District hints a building moratorium may be required. The future of the Sammamish Town Center hangs in the balance.

Lake Sammamish threatened with sewage dump.

By Miki Mullor

The Sammamish Plateau Water District is out of capacity to move raw sewage to King County’s treatment plants.

King County removed a critical sewer line from its projects list that would serve central Sammamish that would transfer waste to a sewage treatment plant in north King County.

A full system and no new project mean development north of a line roughly along SE 8th St. to the border of the Northeast Sammamish Sewer and Water District is in jeopardy. The southern tip of the Northeast district is irregular but roughly follows a line along NE 16th St. and dips south to NE 8th St. in spots.

Future development of homes and the Sammamish Town Center could be blocked by the Sammamish Water District for lack of sewer capacity.

Water Commissioners Lloyd Warren and Mary Shustov hinted that a building moratorium may be necessary if the county doesn’t come up with a solution.

Homes and businesses development in the Northeast sewer district is unaffected by this looming crisis.

County solution waiting since 1987

Warren said records indicate the District discussed sewage flow, called conveyance, as far back as 1987.

Both of jurisdictions have known about this for a number of years, starting in 1987, to “temporarily” move flow to the south, he said.

“Our customers were basically funding the lack of funding by the county. In essence we have been put in this box. Our report said we have no capacity left. We can’t continue to add additional flow to those facilities,” he said. “There still is really no commitment by the county to ensure the facilities will be built.”

A December 7 Technical Memo to the Water District states that “the existing [wastewater] District system is at capacity. Modeling results aside, there is practical evidence that large storm events and short-term intense rain events stress the existing system.” 

A source told The Sammamish Comment that during storm events, the sewage system may see a surge in demand from rain water that enters the system.

The memo explains that Sammamish Plateau Water District staff had to be at the lakefront pumping stations (North Lake and Central Lake Lift Stations, shown on the map below) to manually operate the pumps to achieve their maximum capacity. 

(source: Water District Dec 14, 2020 packet)

“This situation will continue to worsen as Sammamish Town Center continues to develop,”stated the report.

The District’s Comprehensive Plan (2013) explains that “The District sewer collection system flows into and is treated by the King County sewer system. Currently, all flows are directed to the south to Renton (Southern Diversion), but future plans include a second connection to the King County system to the north (North Diversion).”

The areas in pink currently are the areas in Sammamish that currently send sewer south to Renton temporarily until the north diversion pipe is constructed. 

(source: Water District Dec 14, 2020 packet)

New pipe delayed until 2050-2070

The technical memo explains the sudden exhaustion of sewer capacity.

“Planning to this point and time was intended for a pipeline that connected the District’s Inglewood pumping station discharge to a new King County pipeline. King County included the north diversion pipeline project in its 2017 Conveyance System Improvement (CSI) Program, but it was given an estimated project time frame of 2050 to 2070 for project completion, despite determining that the 20-year peak capacity will be exceeded in 2027.”

The Sammamish Plateau Diversion Phase 2 project included over 44,000 linear feet of 27- to 36-inch pipeline along with a 36.6 million gallons per day (MGD) pump station that discharged to the King County system somewhere near Marymoor Park.

(Source: Water District Dec. 14, 2020, packet) 

The King County draft CSI project included a conceptual estimated project cost of $218 million. 

Although it was known since at least 1983 that the northern diversion pipe is needed, and as far back as 2007 was given a high priority status, in 2018 it was downgraded to a lower priority status and pushed out to 2050-2070 timeframe:

(Source: Water District Dec. 14, 2020, packet) 

Immediate action required; Lake Sammamish threatened 

The District concluded that parts of the sewer system are unable to adequately convey present-day peak flows during a large storm event.  The modeling indicates that the North Lake Lift Station may surcharge more than three feet during peak flow times, which means sewage will spill out of the system into the surrounding environment, notably Lake Sammamish.

The District recommends embarking on two projects immediately: 

A $25 million construction of a pipeline pump flows from the Inglewood Lift Station directly to the control structure at SE 43rd Way, mostly along 212th Avenue.  

The length of pipeline required to extend from the Inglewood Lift Station to the control structure on 43rd St. is substantial but it is less disruptive than all alternatives that would require an upgrade of the sewage pipe underneath East Lake Sammamish Parkway. 

The project will also reduce or eliminate odor complaints on Inglewood Hill associated with the current Inglewood pipeline discharge. (This is one of the areas with the most odor complaints and will reduce the chance for overflows in the East Lake Sammamish Parkway area that could flow to Lake Sammamish.  The District estimates it may take up to five years to complete the project.

The District also recommended  $11.8 million to provide relief in the interim in order to prevent spills during severe wet weather conditions.

The project would construct approximately 6,500 linear feet of 16-inch pipeline from the end of the existing North Lake Lift Station, south to  the existing Central Lake Lift Station. 

Potential building moratorium

However, County representatives today acknowledged that there is no budget for interim improvements. There is $3.5 million in the 2021-2022 budget for preliminary design and engineering. But any more must be presented in the 2023-24 budget cycle that has to be approved by King County Executive Dow Constantine in his recommendation to the County Council. The County Council then must approve the project. All-in, the process could take 7-10 years.

Warren was unimpressed.

“From my perspective, we have to assume this is not going to occur,” Warren said. “There are no guarantees. When this board deliberates, which this board will do in the next couple of months, this won’t be an easy decision. But we have been put in a corner and we will have to make some difficult choices.

“We have been patient and we can’t sit back and wait any longer.”

“Has any other district been forced into stopping building for lack of capacity?” Shustov asked. “I don’t want our district to be the exception. Can’t the county give us a solution?”

The County representatives had no answer.

Update: king county’s comment received 12/16/2020:

“Please see the following, sent on behalf of Mark Isaacson, King County Wastewater Treatment Division Director.

I am writing in response to the December 14 article, “Central Sammamish out of sewage capacity; County dumps on development”. The King County Wastewater Treatment Division (WTD) is diligently working with Sammamish Plateau Water District (District) to ensure sufficient sewer capacity for Sammamish. Resolving this issue will require near-term and long-term solutions.

WTD has sufficient capacity in its regional sewer lines, but we funded a consultant study to identify what interim sewer projects can be made in the District’s local sewer lines over the next five years to add sewer capacity for Sammamish. WTD is working with the District to determine the most cost-effective projects that are feasible to construct and bring online in the next few years.

Yesterday’s article states “[n]ew pipe delayed until 2050-2070”. This is not the timeline for the Sammamish Plateau Northern Diversion Project that was deferred during WTD’s 2019-2020 budget process to provide funding for much needed improvements at King County’s West Point Treatment Plant. Predesign work and alternatives analysis work on the Sammamish Plateau Northern Diversion Project will begin again in 2021. Once completed, this project will provide Sammamish with sewer capacity for decades of projected growth. 

At the District’s request, WTD is also in discussions with the District on potentially purchasing almost ten miles of local sewer lines and three lift stations (that pump wastewater flows) as regional sewer facilities, meaning that WTD would then own, operate and maintain these facilities. 

WTD is committed to continue working with the District on these multiple options to meet sewer capacity needs in the near-term and long-term for Sammamish. It is imperative that we provide sufficient sewer capacity in Sammamish in a way that best meets the District’s customer needs and is the best use of the region’s sewer ratepayer dollars.”

Scott Hamilton contributed to this article.

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5 thoughts on “Central Sammamish out of sewage capacity; County dumps on development

  1. Lack of sewage capacity may be finally where the “sh*t hits the fan” to stop excessive growth. Let’s see if this puts a hard stop on development swamping infrastructure. Nothing else seems to be able to stop it.

  2. Oh ? Well, finally the shit hit the fan. Here you can see how poorly the Sammamish City has been managed from the start. Very poor and incompetent leadership had only one vision – rapid growth. 20 years in the making. What other problems will come to the surface next? This is a total shameful history of leadership.

    Sent from Mail for Windows 10

  3. Miki –

    Missing from this analysis is the Northeast Sammamish Water and Sewer utility and their needs and impact on future development capability. They should also be included as Sammamish’s second water & sewer utility.

    Good story!

    Tom O.

  4. Pingback: Sammamish Water District warns Constantine on a development moratorium in Sammamish | Sammamish Comment

  5. Pingback: Sewer connection moratorium enacted on part of Sammamish; current development unimpacted | Sammamish Comment

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