20250402-003: Walnut Creek WWTP Ordinance Staff Report — original pdf

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CIP 3023.046 ORDINANCE AMENDMENT REVIEW SHEET Amendment: Site-specific amendments and related variances Description: Amends Land Development Code (LDC) Chapter 25-1, 25-5, 25-7, and 25-8 and related variances as minimally required to allow the construction of the Walnut Creek Wastewater Treatment Plant Enhancement and Expansion Project Proposed Language: Consider an ordinance granting site-specific variances and amendments to the Land Development Code, including amendments to Chapter 25-1, 25-5, 25-7, and 25-8, as minimally required to allow the construction of the Walnut Creek Wastewater Treatment Plant Enhancement and Expansion Project. Summary of proposed code amendment The amendment under consideration is related to the enhancement and expansion project for the Walnut Creek Wastewater Treatment Plant, especially the construction of a floodwall to protect the facility from flood damage. 25-1 General Requirements and Procedures Amendments to this section are proposed to allow certain variances/waivers to be approved administratively instead of by board or commission. 25-5 Site Plans The project includes several site plans for different project phases and requires a modification to Section 25-5-44 to allow concurrent site plans on the same site. Additionally, the construction of the project will extend beyond the 3-year expiration requirement for site plans so, a amendment to 25-5-81 is also proposed. 25-7 Drainage The construction of the project may require a floodplain variance for which an administrative approval process is proposed. 25-8 Environment A significant portion of the property is located within the 100-year floodplain and the Critical Water Quality Zone of Walnut Creek. The site also has a topography that may require variances to cut/fill requirements and restrictions on regulations. Additionally, there are two identified heritage trees that conflict with the proposed alignment of the floodwall. The proposed amendments to chapter 25-8 include: • 25-8-261 (Development in the Critical Water Quality Zone) to allow for the construction of the floodwall within the CWQZ • 25-8-301 (Construction on Slopes) to allow for administrative approval of the realignment of a roadway on slopes in excess of 15% • 25-8-341 (Cut Requirements) to allow for administrative approval of cut up to • 25-8-342 (Fill Requirements) to allow for administrative approval of fill up to 25 ft 25 ft 1 • 25-8-264 & 25-8-263 (Heritage Trees) to allow for administrative approval of CIP 3023.046 removal of two heritage trees Background: The Walnut Creek Wastewater Treatment Plant (WWTP) receives wastewater flow from Austin Water's wastewater collection system. The plant was originally built in 1977. Over the years, the treatment plant has undergone numerous improvements and upgrades to modernize treatment methods as well as expand treatment capacity to 75 million gallons per day (MGD) with a 2-hour peak flow of 165 MGD. Treated plant effluent is discharged into the Colorado River. A portion of the treated effluent is used for non-potable water (NPW) on the plant site and supplies much of the City’s Reclaimed Water program. This project will expand the plant to treat and discharge an annual average daily flow of 100 MGD and a 2-hour peak flow of 300 MGD. The expansion is needed based on projected future flows of wastewater into the plant, in accordance with the Texas Commission on Environmental Quality (TCEQ) regulations and the requirements of Texas Administrative Code. Additionally, the project will implement Biological Nutrient Removal (BNR) in both the existing and proposed facilities to meet more stringent effluent quality limits in the plant’s discharge permit issued by TCEQ that will go into effect with the expansion. The project includes several distinct components: a new 25 MGD treatment train with BNR, upgrade of the existing treatment to BNR, new peak flow treatment, new influent siphons, new effluent pipe and outfall, and a flood wall around the site. In response to Council Resolution 20250327-062, On March 27th, 2025, the City Council approved Resolution No. 20250327-062 initiating variances and amendment to the Land Development Code, including site-specific amendments to LDC Chapters 25-1, 25-5, 25-7, and 25-8 as minimally required to allow the construction of the Walnut Creek Wastewater Treatment Plant Enhancement and Expansion Project. The resolution directs staff to return an ordinance to City Council on May 1, 2025. Staff Recommendation: Staff recommend approval of the proposed amendments and associated variances with the following conditions.: • The project will be required to seek administrative variances for proposed development that exceeds or modifies the requirements of: • 25-8-301 (Construction on Slopes) • 25-8-341 (Cut Requirements) • 25-8-342 (Fill Requirements) • 25-8-264 & 25-8-263 (Heritage Trees) • For administrative variances granted by this ordinance, the project must demonstrate that no feasible, code compliant design alternatives exist. • The project will be designed to bore the new effluent waterline under Walnut Creek instead of using an open cut channel. • The project extends the CWQZ associated with the southernmost segment of Walnut Creek to an area 150% the size of the proposed impacted CWQZ. • The project commits to relocation of impacted heritage trees where feasible. Board and Commission Actions April 2nd, 2025: To be reviewed by the Environmental Commission 2  Council Action May 8th, 2023: A public hearing will be scheduled. Ordinance Number: TBD City Staff: Leslie Lilly Phone: (512) 535-8914 Email: Leslie.lilly@austintexas.gov CIP 3023.046 3