The BART Warm Springs Extension opened late March 2017 and added 5.4 miles of new track south from the existing Fremont Station. WRECO was responsible for the grading and drainage design for the Warm Springs Station and southern segment of the train tracks from Grimmer Boulevard to the Alameda County Flood Control Channel Zone 6 Line F. Without a proper ratio of permeable to non-permeable surfaces, drainage design can be a tricky and WRECO was responsible for grading, drainage, and water quality treatment for the 26-acre Warm Springs parking lot. WRECO developed a comprehensive grading model of the parking lot using AutoCAD Civil3D. The model was used to set BMP flowlines, check grading criteria, and streamline the drainage system design. The design included over 60 biofiltration swales and 6 bioretention areas with native and drought-tolerant landscaping surrounding the 2,000-space parking lot with native Juncus shade grass. WRECO worked to maximize the treatment area locations, adding and modifying swale footprints to fit best management practices (BMPs) into tight areas. The grass, plants, and trees filter water by removing pollutants before they can be carried into the San Francisco Bay by rain. Because the plants are native and drought-tolerant, they require minimal watering in the summertime.
WRECO also worked with the station architects and mechanical engineers to treat runoff from the roofs of the buildings. WRECO incorporated various unique designs to transmit stormwater runoff to the proposed BMPs by incorporating grading and storm drainage solutions to optimize the treatment. For example, WRECO designed trench drains through the sidewalks to convey runoff from the parking areas to the biofiltration swales on the other side of the sidewalk, along the road. Each biofiltration swale was carefully designed to ensure that the swale areas were reduced where possible to minimize the cost of the BMPs. The final design provided approximately 95% treatment onsite, and the water filtered through the bioswales is re-routed into an underground surge basin. In the surge basin, water can be discharged slowly to prevent overwhelming drainage areas during times of high volume rain.