3003 W CASINO RD BLDG 45-12 2016-10-20

2.1.3 Element 3: Control Flow Rates Describe how you will protect properties and waterways downstream of the project from increased speed and volume of stormwater discharges due to construction activity. Construction of stormwater retention and/or detention facilities must be done as one of the first steps in grading. Assure that detention facilities are functioning properly before constructing site improvements (i.e., impervious surfaces). If applicable, describe how you will protect areas designed for infiltration from siltation during the construction phase. Will you construct stormwater retention and/or detention facilities? ® Yes El No Will you use permanent infiltration ponds or other low impact development (example: rain gardens, bio-retention, porous pavement) to control flow during construction? ❑ Yes® No List and describe BMPs: To protect the properties and waterways downstream of the project site, stormwater discharge volumes from the site will be controlled. The specific BMPs for flow control to be used are listed below. • Existing Storm Drains • Construction Stormwater Chemical Treatment (BMP C250) • Construction Stormwater Filtration (BMP C251) • Existing Pond at SW corner of the site All stormwater generated on site will be diverted to the existing pond, baker tanks, and catch basins in the existing parking lot. A series of site sump pumps and conveyance lines will be installed to collect the water around the site and transport it to the tanks for settling before release. Stormwater collected in the water storage tanks will be tested for pH and turbidity and to meet the constituents and testing protocols identified in the Washington State Department of Ecology Administrative Order before discharge. Installation Schedules: The sediment tanks will be installed on-site at the S-4 parking lot at the start of construction.. Inspection and Maintenance plan: The existing pond will be inspected daily to ensure turbid water is not leaving the site. Page 1 11