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Red Morton Park Regional Stormwater Capture Project Redwood City, CA Task 3. Preliminary Design Concepts Report This task encompasses the integration of the collected site data and preliminary studies to evaluate project alternatives including diversion points/rates, project footprints, and outflow evaluation. Task 3.1. Alternative Evaluation & Feasibility At the onset of this task, the Consultant will develop project objectives and constraints relative to the project goal of multi -beneficial, innovative, and efficient regional stormwater capture. Working with the City, the Consultant will work to establish recommended measures of performance for each project objective, which will include the operation and maintenance costs, present capital costs, service life, scale to cost relationships, and park impact minimization. The Consultant has developed a suite of tools that provide a state -of -the -science system for hydrologic and water quality assessments to support design. Regional stormwater capture sizing will be conducted in EPA SUSTAIN to support the design of stormwater capture capacity alternatives. The Consultant will simulate three (3) alternatives that will consist of multiple configurations to conduct a Best Management Practice (BMP) Optimization Analysis that will identify the following design parameters for the optimal BMP design: BMP Sizing & Siting Options o BMP size that will capture the 85th percentile, 24-hour storm volume o BMP size that will achieve multi -benefits, including, but not limited to, addressing stormwater quality and water supply. • Diversion Flow Rates o Multiple diversion flow rates will be simulated to develop cost effectiveness curves o The optimal diversion rate will be determined based on the point of declining water quality benefit • Outflow uses and flow rates o On-site irrigation potential o Exfiltration options (infiltration, sanitary sewer discharge, or filtration units) The approach will develop recommendations for the BMP location, footprints and cross-sections, and type and size of pre-treatment systems and diversion structures for the design configurations. Additionally, the park impacts will be summarized for each alternative to provide the anticipated public use impacts. The evaluation results and summary will be incorporated into the Preliminary Design Concept Report in Task 3.4. Task 3.2. Preliminary Layouts As part of the Alternative Evaluation in Task 3.1, the Consultant will develop 10% preliminary site layout sketch(es) of up to three (3) alternatives showing the location of the diversion, valve(s), pretreatment unit(s), pump station, conveyance lines, storage structures and any other overflow/return lines or filtration/treatment systems. The exhibits will be prepared on 11"x17" plans and will show the plan layout, as well as the profile of the system. The preliminary elevations will be necessary to best estimate the requirements of the pump station and earthwork quantities. The preliminary site layout will be submitted to the City Project Manager for review and preliminary comments. The site layout will be used as the basis for conducting the BMP Optimization, Diversion recommendations, and water quality pollutant load reduction. Task 3.3. Preliminary Estimate of Probable Costs The Consultant will prepare a preliminary construction cost estimate for each of the three alternatives. The cost estimates will be based on the preliminary concept developed. The cost estimate is considered preliminary and it is used for budget authorization or budget control purposes only. This cost estimate will only include major ATTY/AGR.2020.309/Craftwater Inc (Page 17 of 34)