2019-040 - Mainplace Mall Transformation

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Kimley>»Horn Existing Local Infrastructure: The site generally drains to three separate storm drain syste ms: Main Street Strom Drain System: The City owns and maintains an existing 36" to 42" diameter storm drain pipe in Main Street, immediately east of Mainplace Mall. The pipe drains from north to south and discharges into Santiago Creek. Mall drainage, other private development drainage, and City street drainage are commingled in this drain. Caltrans South Drainage System: When Caltrans widened Interstate 5 and State Route 22 for the 5/22 interchange project, it replaced a significant amount of local City drains with Caltrans drains within Caltrans right-of-way. Included is a small local storm drain network that drains southerly to Santiago Creek. This system commingles City drainage, Caltrans drainage from the northbound Interstate 5 lanes, and drainage from a portion of the mall. Caltrans North Drainage System: Caltrans owns and maintains a substantial amount of drainage infrastructure for the 5/22 interchange project, with significant pipes, channels, and box culverts. The Caltrans north drainage system accepts local street drainage, private development drainage, including from Mainplace Mall, and freeway mainline and interchange drainage. This system discharges directly to Santa Ana River at the State Route 22 bridge over the River. Existing Site Infrastructure and drainage pattern: The site is served by an existing storm drain system discharging to six different locations. On -site drains range in size from 12" to 30" diameter. A storm drain system in the on -site ring road primarily accommodates drainage from the existing mall building. The site surface lots generally drain away from the mall building toward Mainplace Drive on the west and north sides of the Mall and toward Main Street on the east side of the mall. A more detailed description of drainage patterns and connection points follows: Discharge Point A (CP-A): Approximately 19.2 acres of the site, including the mall building, drains into the existing on -site loop road storm drain and into an existing 30" City reinforced concrete pipe (RCP) that runs northwest under Mainplace Drive. The City RCP discharges into the adjacent Caltrans North drainage system. Discharge Point B (CP-B): Approximately 11.2 acres of the northwest portion of the site, including most of the two existing parking structures in the northwest quadrant, drains to an existing 30" City RCP that runs northwest under Mainplace Drive. The City RCP Page 6 of 14