The District's first sewer collection and treatment system was constructed to serve the Frontier Village Complex and was financed and built by developers. This system was constructed in 1965. The initial treatment facility consisted of a 1.4 acre oxidation pond which is still used today in a modified form in the treatment process.
In 1971, the District expanded it's collection system through Utility Local Improvement Districts (ULID) 1 and 2. These projects were constructed with the aid of EPA funding. ULID 1 follows the lake shoreline and extends from the southern tip of the lake to the northwesterly shore. The City of Lake Stevens discards its wastewater into the District's facilities at the northern portion of this ULID system. ULID 2 provides collection service along the corridor of 91st Avenue Northeast (Hillcrest Drive), from Vernon Road to 11th Place Southeast. The District's first wastewater treatment plant expansion was also constructed at that time. The plant expansion included the addition of an 8.5 acre lagoon cell to be used in parallel with the existing 1.4 acre cell.
The City of Lake Stevens (City) entered a Joint Participation Contract with the District in 1970 to allow discharge of sewage to the District's collection and treatment system which was to be constructed as part of ULID 1. This contract defined the quantity and quality of the sewage to be discharged to the District. The contract has been subsequently revised and or amended in 1983, 1986, 1991 and 1996. A copy of the current Sewage Disposal Agreement between the District and the City is included in Appendix A.
ULID 3 was formed in 1980 to serve the east side of the lake south of the City of Lake Stevens. The construction of this ULID nearly completed the collection system coverage of the perimeter of the lake.
In the mid-1980's the District wastewater treatment plant was expanded a second time. This expansion included head works, the partitioning of the 1.4 acre oxidation pond into 2 aeration basins and 2 anaerobic digesters, the addition of 2 final clarifiers and the addition of a Chlorine contact tank.
In the early 1990's, ULID 7 & 8 were formed west of the lake. Both of these ULIDs serve the eastern corridor of State Route 9, between 4th Street Northeast and 12th Place Southeast.
Lift Station 12 was constructed and placed on-line in the spring of 1998. This allowed service for the southern portions of the Lake Stevens drainage basin, on both the east and west sides. This project was funded by the District though a combination of revenue bonds and a Public Works Trust Fund loan.
The number of District Equivalent Residential Units ((ERU) has increased from 1,000 in 1983 to 5,395 in 1999 with continued growth and development we currently have 13,511 ERU as of April 2020. The growth has been accommodated by expansion of the sewer system funded predominately developer extension projects.
In 2005, the District entered into the Unified Sewer Agreement with the City to operate and maintain all sewer collection and treatment facilities within the entire Lake Stevens Urban Growth Area ("UGA"), both unincorporated area and the City.
The District currently operates 125 miles of collection system, 12 miles of interceptor and 29 lift stations and the new (April 2013) treatment plant is located adjacent to 9th Street SE and Sunnyside Boulevard above the Snohomish River floodplain. The treatment process has been upgraded to (Membrane BioReactor) technology with UV disinfection. This significantly improves the quality of the effluent discharged to Ebey Slough. The new plant is designed to have a capacity of 5.01 MGD (maximum month flow), less than 2mg/L BOD, less than 1 mg/L TSS and less than 1 coliform colony/ 100mL. The new WWTF collects methane, a greenhouse gas, from the Anaerobic Digester and burns as an energy source for the plant operation, reducing power requirements from the public utility. The new Sunnyside Treatment Plant facility provides adequate wastewater treatment and disposal to the District’s service area through the year 2028, with provisions for upgrades to serve build-out conditions. Upgrade will be deffered until the anticipated growth happens.
The District serves a drainage area of approximately 4500 acres surrounding Lake Stevens. The District’s Comprehensive Plan outlines District sewer service to a total of 17,312 acres in and around the Lake Stevens UGA. 6,862 acres are currently within the Lake Stevens UGA. Growth through annexation to the District is accomplished either by annexation into the City or into the District by provisions under Title 57 for Special Purpose Districts followed by formal hearings and ultimate approval of the Snohomish County Boundary Review Board or referendum vote of those being annexed.