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Water Quality Management Plan (WQMP) <br />Mainplace Mall Specific Plan <br />Main Street Strom Drain System: The City owns and maintains <br />an existing 36` to 42" diameter storm drain pipe in Main Street, <br />immediately east of Mainplace Mall. The pipe drains from north <br />to south and discharges into Santiago Creek. Mall drainage, <br />other private development drainage, and City street drainage <br />are commingled in this drain. <br />Caltrans South Drainage System: When Caltrans widened <br />Interstate 5 and State Route 22 for the 5/22 interchange project, <br />it replaced a significant amount of local City drains with <br />Caltrans drains within Caltrans right-of-way. Included is a <br />small local storm drain network that drains southerly to <br />Santiago Creek. This system commingles City drainage, <br />Caltrans drainage from the northbound Interstate 5 lanes, and <br />drainage from a portion of the mall. <br />Caltrans North Drainage System: Caltrans owns and maintains <br />a substantial amount of drainage infrastructure for the 5/ 22 <br />interchange project, with significant pipes, channels, and box <br />culverts. The Caltrans north drainage system accepts local street <br />drainage, private development drainage, including from <br />Mainplace Mall, and freeway mainline and interchange <br />drainage. This system discharges directly to Santa Ana River at <br />the State Route 22 bridge over the River. <br />............................................................................................................................................................................................................................................................................................................................. <br />Orange County Hydrology Manual soils type B. Preliminary <br />Soil Type, Geology, and <br />geotechnical investigations and testing indicate that the top 30 <br />Infiltration Properties <br />feet of soils are generally impermeable and not feasible for <br />infiltration. The soils below the top 30 feet are granular in <br />nature and feasible for infiltration. <br />Hydrogeologic <br />Preliminary geotechnical investigations and testing indicate a <br />(Groundwater) <br />water table in excess of 100 feet below ground surface. <br />Conditions <br />However, the historic high water is in the range of 3040 feet <br />below ground surface. <br />Two infiltration tests were taken at the site at a depth of 10 feet <br />to 15 feet. One of the infiltration tests had and adjusted <br />Geotechnical Conditions <br />infiltration rate of 0.64 inches per hour and the other had an <br />(relevant to infiltration) <br />adjusted infiltration rate of 0.54 inches per hour. Below a depth <br />of 30 feet, the soils are more favorable for infiltration, though the <br />historic high water reaches to the top of these soils. It is <br />assumed at this time that near -surface infiltration will be feasible <br />Error! Reference source not found. Section III <br />Conceptual Specific Plan WQMP 2019.04.24 - WQMP.docx Page 17 <br />