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Water Quality Management Plan (WQMP) <br />Mainplace Mall Specific Plan <br />Approximately 8.9 acers of the North-west portion of the site drain to an <br />existing 30" RCP that crosses Mainplace Drive and connects to the adjacent <br />Caltrans drainage system. Approximately 19.1 acers, including the existing <br />mall building drains to an on -site storm drain system that surrounds the mall <br />building and connects to the adjacent Caltrans drainage system. The south- <br />west parking lot, approximately 6.2 acres, drains to a catch basin that connects <br />to the adjacent Caltrans drainage system. These areas, totaling approximately <br />14.8 acres, are tributary to the Caltrans drainage system which in turn <br />discharges to the Santa Ana River. <br />In the proposed condition, drainage will flow away from the proposed and <br />existing buildings and into one of several low points across the site. The <br />existing storm drain infrastructure will largely remain in use. New inlets will <br />tie into the existing storm drain lines as each phase comes online. <br />Approximately 580' of offsite storm drain extension in Mainplace drive will be <br />required to support the proposed development. The site drainage pattern will <br />largely match the existing drainage pattern and will not significantly increase <br />tributary area to any of the existing storm drain connections. <br />Centennial Section II <br />Conceptual Specific Plan WQMP Page 5 <br />