20200415-008c: Davis Water Treatment Plant PC-2012-0414(R1) REVISED presentation — original pdf

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DAVIS WATER TREATMENT PLANT – ZEBRA MUSSEL MITIGATION PROJECT 3352 MOUNT BONNELL ROAD SPC-03-0414(R1) Scott E. Hiers, P.G. Hydrogeologic Reviewer Watershed Protection Department And Pamela Abee-Taull Environmental Review Specialist Senior Development Services Department This product is for informational purposes and may not have been prepared for or be suitable for legal, engineering, or surveying purposes. It does not represent an on-the- ground survey and represents only the approximate relative location of property boundaries. This product has been produced by the Watershed Protection Department for the sole purpose of geographic reference. No warranty is made by the City of Austin regarding specific accuracy or completeness. PROPERTY DATA • Lake Austin Watershed • Water Supply Suburban &Rural Classification • Drinking Water Protection Zone • Full Purpose • Over Edwards Aquifer Recharge Zone • Critical Environmental Features on site • Council District 10 This product is for informational purposes and may not have been prepared for or be suitable for legal, engineering, or surveying purposes. It does not represent an on-the- ground survey and represents only the approximate relative location of property boundaries. This product has been produced by the Watershed Protection Department for the sole purpose of geographic reference. No warranty is made by the City of Austin regarding specific accuracy or completeness. BACKGROUND • To provide Zebra Mussel Mitigation at the raw water in-take using low concentration of copper sulfate pentahydate (CuSO4 · 5H2O). • Double-walled chemical storage, canopy and metering system to the low service pump station (LSPS). CODE REFERENCE Title 25 – Land Development Code, Chapter 25-8-281(C)(2)(b) and 25-8-341. VARIANCE REQUEST 1. Request to vary from LDC 25-8-281(C)(2)(b) to allow the construction Zebra Mussel Mitigation System within 150-foot Critical Environmental Feature (CEF) buffers. 2. Request to vary from LDC 25-8-341 to allow cut exceeding 4 feet, to 5.5 feet. VARIANCE RECOMMENDATION Finding of Facts have been met. Approval of variance with following condition: • Additional wetland mitigation will be installed per Code, no special conditions. The requirement will deprive the applicant of a privilege available to owners of similarly situated property with approximately contemporaneous development subject to similar code requirements. Yes. Other City of Austin water treatment plants have the same chemical feed system in place to help control zebra mussel infestations in the raw water transmission main. Chemical treatment is necessary infestations in raw water to control zebra mussel transmission mains. Is not necessitated by the scale, layout, construction method, or other design decision made by the applicant, unless the design decision provides greater overall environmental protection than is achievable without the variance; Yes. The variance is not necessitated by the design. No alternative locations are available on site for a Zebra Mussel Mitigation System. The system must be placed in or near the existing intake pump house. There is not enough room in the existing pump station to house the entire system, such as the chemical storage. All the proposed construction coincides within areas of existing impervious cover. Minimal additional impervious cover is being added. Is the minimum deviation from the code requirement necessary to allow a reasonable use of the property; Yes. The variance is a minimum deviation from the code requirement and is allowing for a reasonable use of the property. No new impervious cover is proposed. The Zebra Mussel Mitigation System and the associated construction activities is in areas, or adjacent to areas, with existing impervious cover or development. The piping for the chemical storage and metering station is the shortest and most direct route to the existing building, and the system is located where there is already an asphalt driveway or development. Does not create a significant probability of harmful environmental consequences. a probability of significant harmful Yes. The variance with the staff recommended conditions does not create environmental consequences. Construction is within existing structures or where there is existing impervious cover. The chemical tank and piping are double contained. The equipment pad is curbed and covered with a canopy. The pump metering station includes a virtual day tank and there are automated valves at the pump bay that close if the pumps fail or when the pumps are not running. No new impervious cover is being added. As part of the Stormwater Pollution Prevention Plan, temporary sedimentation and erosion controls will be installed prior to the start of construction activities. The applicant is providing wetland plantings along the shoreline that will reduce shoreline erosion and reduce the possibility of sediment-laden surface runoff from entering the lake. Development with the variance will result in water quality that is at least equal to the water quality achievable without the variance. Yes, the variance will result in water quality that is at least equal to the water quality achievable without the variance. The proposed construction will not impact existing water quality. No new impervious cover is proposed. During construction, Stormwater Pollution Prevention Plan best practices will be employed to prevent construction sediment and debris from entering the stormwater runoff, and additional wetland plants along the shoreline will be provided to enhance the water quality of surface water runoff.