Wasilla council hears plan to use adjacent wetlands for treated effluent and to upgrade sludge handling

Wasilla City Council members on May 19 heard from Stantec Consulting about a two-part plan to relieve capacity limits and reduce groundwater impacts at the Wasilla Wastewater Treatment Plant.

Dean Sido, a Stantec consultant, told the council the plant is “presently permitted for approximately 400,000 gallons per day” and is “pushing up against that permit limit,” and proposed a wetlands discharge system and related upgrades that Stantec says could increase permitted disposal to 500,000 gallons per day.

The discussion matters locally because the plant’s existing percolation beds have largely failed and excess effluent is reaching groundwater. “So right now, the effluent that is applied into the beds, is essentially being directed to the groundwater below the water plant, which is putting some of the nitrate and ammonia constituents into the groundwater,” Sido said during his presentation.

Nut Graf — why this matters: City staff and the consultants said the proposal aims to buy time and reduce environmental risk by routing treated effluent through vegetated wetlands that can “consume the nitrates, the ammonia, the various nutrients from the wastewater,” according to the presentation. The plan also includes separate work to expand sludge digestion, add mechanical dewatering and modernize operations to reduce odors and cut reliance on the existing drying beds.

Key points and timeline

- Permit and approvals: Stantec has applied for a U.S. Army Corps of Engineers Section 404 permit (wetlands permit) and reported the application is in legal review. Sido said, “We are probably 1 or 2 months away from achieving that permit.” Once the Corps permit is issued, the city would acquire easements or property, seek Alaska Department of Environmental Conservation (DEC) approval to construct, then apply for a state discharge permit.

- Capacity: The wetlands discharge facility is intended to support 500,000 gpd — 100,000 gallons more than the current permit — while a separate recommendation and future projects would be needed to reach still higher flows.

- Cost and schedule: Stantec estimated the wetlands treatment facility at roughly $2,000,000 or less. The consultants said design is approaching completion; they expected construction documents to be ready by February (design year) and possible construction in 2026–2027, with exact phasing dependent on funding.

- Sludge handling: Stephanie Schiebel of Stantec outlined a sludge project funded in part by an EPA grant. The preliminary engineering report (PER) covers alternatives including an additional digester, batch digestion to improve residence time, and mechanical dewatering to produce a drier “cake” that reduces the liquid fraction returned to lagoons and the groundwater.

- Odor and drying beds: Consultants and operations staff said odors are driven by decanting to drying beds that mix well-digested and fresh sludge. Mechanical dewatering was presented as a way to produce a higher-quality solid year-round and reduce odor complaints in nearby neighborhoods.

- Pilot testing and monitoring: The city conducted a three-year pilot test of wetlands discharge in 2016–2019 (transcript indicates pilot sampling in 2018–2019). Stantec proposes offering annual drinking-water sampling to private wells within roughly a half-mile of the plant for two years and then reevaluating, responding to residents’ concerns.

Technical constraints and questions raised by council

Council members pressed consultants on several technical and regulatory points: how “wetlands” are being defined (federal and state definitions can differ), why the existing percolation beds failed (consultants said a thick silt layer under the beds acts as an aquaclude, so the beds saturate at modest flow rates), and how much additional capacity wetlands can realistically accept before channelization damages vegetation.

Consultants said the existing percolation beds operate at about 25% of the needed capacity; they estimated the beds begin to fail when flows exceed roughly 80,000–100,000 gpd applied to those beds. The proposed diversion structures and short dikes (4–6 feet of structure, about 2 feet visible above ground) are designed to route flow through specific wetland paths without substantially altering wetland hydrology.

Sludge, septage and receiving capacity

Stantec told the council that the plant currently handles a large quantity of septage and that some haulers are sent to Anchorage when Wasilla cannot accept all loads. The consultants reported the plant is handling roughly 1.3–1.4 million gallons of septage in the current reporting period and that the sludge facility is at capacity — a driver of the push to add digestion and dewatering equipment.

“The goal minimum is to make sure that you’re handling what you should be handling today,” one consultant said, describing near‑term upgrades to reduce diversion of local customers’ waste to off-site facilities and to reduce operational strain on lagoon processes.

Treatment technologies and winter performance

Stantec recommended comparing options for winter ammonia treatment and for future higher-capacity treatment at end-of-pipe, including a submerged attached growth reactor (SAGR) (a buried media system that stays warm and treats ammonia year‑round) and a moving bed bioreactor (MBBR), a compact—but energy-intensive—technology. The consultants noted wetlands perform well in warm months but have limited winter capacity and that DEC is likely to require ammonia treatment for expanded discharge, especially in winter.

Community protections and property issues

Consultants said the Corps permit, if issued, would remove the designated wetland area from federal wetland inventory and reclassify it as a permitted wastewater facility; the city also needs easements or acquisitions to clearly delineate the permitted boundary. Stantec emphasized they are not proposing to “inundate” or raise wetland water levels and said they will mark the facility with signage rather than fencing to minimize wildlife impacts.

Public concerns about well sampling, odors and truck traffic were raised during the presentation. Stantec said no private well sampling has occurred since the pilot was discontinued about 18 months ago and offered the proposed annual sampling program to properties inside the gray half‑mile box shown in the presentation.

Council actions and next steps

Council member motions during the meeting included a procedural move (by Council member Crafton) to take sewer treatment permitting discussion during the Stantec presentation; the council then discussed budget ties to the projects. Consultants and staff described a two-track approach: (1) proceed with the Corps 404 and DEC permitting and the wetlands discharge work to secure another 100,000 gpd of permitted disposal at relatively modest cost, and (2) pursue sludge upgrades and further treatment technologies in a master plan for future expansion.

What remains unresolved

Stantec and staff said the project depends on the Corps 404 permit and easement acquisitions; if the Corps were to deny the 404 permit, the city would need to accelerate higher‑quality end-of-pipe treatment on site and could not rely on the wetlands polishing approach. Consultants also flagged the need for additional funding to move beyond the 500,000 gpd level and noted construction phasing will depend on available grants and capital.

Ending — immediate follow-ups

Stantec left the council with specific near-term tasks: pursue the Corps of Engineers 404 review (app currently in legal review), finalize easement and property agreements, complete the sludge PER funded by an EPA grant, and prepare construction documents. The consultants also urged the city to run updated customer and growth projections so future treatment capacity can be planned into a master plan that links effluent, sludge handling and possible ammonia treatment options.