Environmental commission backs land‑code changes for Walnut Creek wastewater plant expansion with conditions

The City of Austin’s Environmental Commission on April 2 recommended that the City Council approve site‑specific amendments to the Land Development Code needed to allow the Walnut Creek Wastewater Treatment Plant Enhancement and Expansion Project, but the commission attached conditions addressing environmental mitigation, tree preservation, energy, public access and ongoing monitoring.

Watershed Protection staff and Austin Water officials told the commission the project would expand the plant’s permitted capacity by 25 million gallons per day — from 75 million to 100 million gallons per day — and convert existing treatment processes to biological nutrient removal. Charles Solaro, assistant director with Austin Water, said the upgrades aim to reduce nutrient discharges and modernize aging infrastructure. “We will reduce phosphorus at a minimum of about 60% from current discharge levels and substantially increase nitrogen removal,” Solaro said during the presentation.

The commission’s recommendation follows Council Resolution No. 20250327‑062 initiating the code amendments and is tied to Capital Improvement Project No. 203023046. City staff described multiple land‑use exceptions they say are “minimally required” for construction: allowing a flood wall into the Critical Water Quality Zone (CWQZ), administrative approval of variances for cut‑and‑fill and slopes, administrative handling of potential heritage‑tree removals, and flexibility for multiple site plans and floodplain variance procedures during project delivery.

Why it matters: Austin Water says the plant has approached operational limits in recent years and modeling and flow data indicate the city could exceed the plant’s current permitted capacity within the next decade unless upgrades proceed. The expansion is a large capital project (city staff stated the estimated cost is about $1 billion) and affects waterways that feed the Colorado River and local creek corridors. Commissioners and members of the public focused on protecting downstream water quality, preserving tree canopy, floodplain impacts and public access to nearby trails and riverfront.

What the commission recommended: The Environmental Commission’s motion — adopted with one opposing vote — asks City Council to amend multiple sections of the Land Development Code to enable the project, and it attaches 15 conditions. Key staff‑recommended conditions that the commission retained or expanded include: - Require administrative variances for construction on slopes, cut and fill in excess of code limits, and potential heritage tree removal, with the stipulation that the applicant must demonstrate no feasible code‑compliant alternatives. - Design the new outfall and effluent conveyance by boring/tunneling under Walnut Creek (not open‑cut) to minimize tree removal and surface disturbance. - Extend the CWQZ downstream by dedicating additional CWQZ land at a ratio the motion set at 150% (the commission adopted an amendment asking staff to explore increasing that to 200%). - Commit to relocating impacted heritage trees where feasible, with required feasibility analyses and five‑year care plans for any transplanted trees.

Commissioners added conditions during debate that the project team must report back annually to the Environmental Commission on progress, and that staff pursue additional environmental and community measures including: increased public outreach and interpretation about the facility and trails, both a requirement for low‑carbon ("green") concrete on the project and exploration of on‑site or adjacent solar generation where feasible, expanded downstream nutrient monitoring beyond TCEQ minimums, testing plans for PFAS once accepted testing methods and regulatory guidance are available, and exploration of transferring up to 50 acres of underused property for public open space or park use where feasible.

Project details and constraints presented by staff: Leslie Lilly, environmental conservation program manager with Watershed Protection, said the plant sits inside city limits north of the Colorado River and is partially in the 100‑year floodplain and CWQZ. The flood wall is proposed to protect the plant from flood damage; staff said wall height will be informed by hydraulic modeling (Watershed/Atlas 14 data) and could vary across the site. Austin Water said the wall will likely require deep foundations to prevent underflow and that tunneling for the outfall better preserves the riparian trees than an open cut would.

Public comment and concerns: Bobby Levinsky of the Save Our Springs Alliance urged commissioners to delay endorsements until more detail was available on the variances, critiqued the project’s transparency in agenda backup, and said more emphasis on demand management and conservation could reduce the need for large capacity expansions. Commissioners asked staff about operational phasing — so expansion capacity can be brought online while existing trains are converted — potential environmental effects of adding treated flow, noise and trail access, tree‑relocation feasibility, endangered‑species and permit review steps, and energy use implications of the new biological nutrient removal process.

Votes and next steps: The commission voted to recommend the code amendments to council with the full set of staff conditions and the additional amendments the commission adopted (annual reporting to the commission; low‑carbon concrete; exploring on‑site solar and parkland transfer; exploring expanded CWQZ dedication; and PFAS testing guidance). The recommendation is advisory; final authority to change the Land Development Code and approve variances rests with City Council. Austin Water and Watershed staff said site plans and environmental reviews will continue and that administrative variances would be considered during site‑plan review in keeping with the conditions the commission requested.

Ending: Austin Water and Watershed staff said they will return with further details in site plan reviews and that technical studies (hydraulic, ecological, tree‑relocation feasibility and nutrient modeling) are ongoing. The commission’s recommendation will be transmitted to City Council as part of the council ordinance and code‑amendment process.