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5) Analyze internal drainage structures, including storm drain systems and culverts for <br />the design storm and 100 -year check storm. <br />1.7.9 Storm Drain Design. <br />1) Analyze design of both open channel (ditches) <br />accordance with guidelines provided in the HDM. <br />2) Provide drainage design details for "non- standard" <br />where TxDOT standard details cannot be utilized. <br />1.7.10 Storm Water Oualitv Facilitv Analvsis Design. <br />and enclosed storm drains in <br />drainage structures in instances <br />1) Perform analysis and design of water quality control facilities within the Project <br />ROW in accordance with TCEQ design criteria for treatment of runoff from increased <br />impervious cover. <br />2) Perform a feasibility study, analysis, and design of additional water quality control <br />facilities outside of the ROW in accordance with City of San Marcos /City of Austin <br />design criteria for treatment of runoff from existing impervious cover. <br />1.7.11 Storm Water Detention Analvsis and Design. After the Engineer completes the H &H <br />analysis and design (as detailed above) and the hydrologic and /or hydraulic impacts are assessed, <br />the Engineer will prepare a single mitigation plan based on utilizing one or more detention <br />facilities within the ROW and under the Loop 82 overpass bridge to mitigate impacts taking into <br />consideration hvdrologic impacts - increases in peak flow rates outside of TxDOT or City ROW <br />or drainage easements. It is TxDOT's preference to locate any structure intended for mitigation <br />(ponds, energy dissipaters, etc.) inside of TxDOT's ROW. <br />1.7.12 Storm Water Pollution Prevention Plan (SW3P). <br />1) Both the City and the Engineer understand that temporary storm water management <br />devices will be necessary to minimize the sediment runoff during construction of this <br />Project. The Engineer will develop a temporary erosion and sediment control plan for <br />the length of the Project that complements the design and construction phasing of the <br />Project, and will include notes that indicate that the construction contractor is <br />responsible for detailed sequencing of the devices. The Engineer will utilize the <br />following design components: <br />a) Non - disturbance area delineation (preserving existing vegetation); <br />b) Temporary and permanent vegetation seeding or sodding; <br />c) Erosion control blankets; <br />d) Diversion dikes or swales; <br />e) Temporary mulch; <br />fl Silt fence; <br />g) Sand bags; <br />h) Rock filter dams; <br />HDR— Loop 82 Project Agreement <br />21 <br />