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Red Morton Park Regional Stormwater Capture Project Redwood City, CA • Earthwork recommendations including engineered fill placement and utility trench backfill. Task 2.5. Hydrogeological Study (OPTIONAL) Based on previous information, the Consultant has either reviewed or published for the Red Morton Community Park site, the subsurface can be characterized as having a highly impermeable surficial soil layer overlain by a more porous gravel layer at approximately 15 feet in depth. Based on the Consultant studies, Consultant anticipate average groundwater depth to be approximately 10 feet. However, some down -gradient areas of the park contained permeable sands as close as 8 feet below existing ground near where Phase 1 is indicated in the RFP. This area may be suitable for an open bottomed infiltration/recharge scheme if piped from an upstream area. This task will be performed by Consultant following written notice from the City. Hydrogeological Study Evaluation. Consultant recommends that after a preliminary concept for the water capture project has been developed, a hydrogeological evaluation be performed. The scope may vary depending on the exact nature of the preferred alternative project. Consultant assumes that it will perform the following: 1) Installation of a minimum of two monitoring wells at upgradient and downgradient locations to monitor changes in the uppermost aquifer units during wetting and drying cycles during one water year. 2) Providing a MODFLOW model of subsurface conditions, which incorporates geotechnical and hydrogeologic data to estimate infiltration and potential recharge rates in wet and dry scenarios at the site of the preferred alternative. Optional Aquifer Pumping. Potentially constructing a 4 -inch diameter monitoring well and performing pumping tests to characterize transmissivity, storativity, permeability, and distance of influence of the proposed site. Task 2.6. Utility Research Utilizing USA North 811's website, a comprehensive utility matrix will be developed, which the Consultant will use to request utility atlas information. The atlas information will be used to prepare an existing utility index map for the project area. Once the site investigations and project information review component are complete, the Consultant will perform a site visit to verify the accuracy of data obtained and the locations of the utilities based on the utility atlases received. The team will also verify the appropriate right-of-way and incorporate the utility investigation into the topographic base maps. The underground utility locations will be identified and incorporated in the existing site plan. This information will be used in verifying the preliminary design layouts and minimizes utility conflicts. Task 2.7. Hydrologic and Hydraulic Study This task will consist of evaluating and modeling the potential drainage area that could be captured by the Red Morton Community Park project. The drainage area will be delineated using the most recent countywide LiDAR data (assumed to be provided for this project) and compared to the initial concept drainage area. For the project drainage area, the Consultant will update and summarize the critical storm sequence, flow rates, and volumes to meet the Total Maximum Daily Loading (TMDL) and volumes/loading identified in the initial project concepts. The study will serve as the inflow and baseline for the alternative analysis in Task 3 to measure possible pollutant reduction. The Consultant will utilize the existing hydrologic and hydraulic models prepared for the County Reasonable Assurance Analysis as a starting point. Modeling will be updated using all available data. Results from the Hydrologic and Hydraulic Study will be summarized in a memorandum. A draft will be submitted and all comments will be addressed and prepared in a final document. Task 2.8. Hydraulic Modeling The hydraulic modeling analysis will evaluate the wet weather flows of the existing storm drain system. The models will be set up to evaluate both the 24-hour design storm events (85th percentile, 10 -year, and 100 -year) ATTY/AGR.2020.309/Craftwater Inc (Page 15 of 34)