Ord 2011-021 - Laserfiche WebLink

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• Capture rain water and condensate for use in irrigation • Sizing and technical details to be based on TCEQ or City of Austin criteria TCEQ and City of Austin (COA) criteria and technical manuals identify several types of water quality control facilities that achieve 85% TSS removal. These facilities include retention/irrigation systems, vegetative filters, sedimentation/filtration systems, wet ponds, bio- filtration or bio - retention systems, rain water harvesting, rain gardens, porous pavement, bioswales, and "proprietary" compartmentalized systems. In consideration of the location and layout of the proposed development, site topographic constraints, practicality of control facilities as relates to constructability, maintenance, and cost, and the criteria listed above, a combination of a bio - filtration or bio - retention system, rainwater harvesting, and bioswales are proposed. A bio - filtration (COA nomenclature) system or bio - retention (TCEQ nomenclature) system will comprise the main. permanent water quality control. This facility will be sized to provide treatment for all impervious cover on the site. Per both TCEQ and COA criteria manuals this type of system is rated to remove 89% of TSS. This system will be located along the south side of the building. Tables 1 and 2 provide calculations for the water quality volume for this type of system based on TCEQ and COA criteria respectively. Figures 1 and 2 show the location of this system as sized and configured per TCEQ and COA criteria respectively. It should be noted that the layout of these systems as depicted in Figures 1 and 2 is schematic and is intended to depict relative size and relationship to the proposed development. Adjustment and layout within the constraints of the design criteria to achieve a less obtrusive or more esthetically pleasing effect can be better addressed during development of detailed construction plans. In addition to the bio - filtration or bio - retention facilities rain bioswales will be utilized in the surface parking area and rain water harvesting will be used in the building area. The use of these facilities is further described in the following section of this report titled "Low Impact Design Landscape Strategies for Chestnut Street Lofts in San Marcos, Texas" as prepared by J. Robert Anderson, Landscape Architects. This section follows the Figures in the first section of the report. DETENTION. As a result of the anticipated, proposed building finished grade and the existing topographic drop across the building footprint between the northwest and southeast building comers, the bottom of the lowest garage floor will be approximately 15'— 20' above natural ground. About 25% of the building at the southeast comer will be above natural ground. It is proposed to locate a detention chamber in this space below the lowest garage floor. Detention calculations are provided in Table 3. The relative size and location of the detention chamber is shown on Figures 1 and 2. OUTLET CONTROL. Concentrated storm -water flows from the parking area and the building will be conveyed to the bio - filtration facility via piping. Similarly concentrated outflows from the bio - filtration facility will be conveyed to the detention chamber via pipe or channel. Concentrated outfall flow and overflow from the detention pond will be released either via piping to the bottom of the existing channel along the east side of the Project site or via a pipe placed on a flat grade in a southerly direction and ending in a