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Approximately 25 acres of the project site would be mostly covered with impermeable surface materials after construction is complete. The addition of impermeable surfaces could increase runoff velocity and quantity, and thereby increase the potential for erosion at the site and downstream without preventive action. The storm water drainage plan for the project incorporates a series of detention ponds or swales to contain and slow runoff from the project site (per current WSDOT standards). By collecting, conveying, and slowing down water from typical 2-, 10-, and 100-year, 24-hour storm events, the potential for on-site and downstream erosion during project operation would be minimal. The proposed recreation and hospitality facility incorporates a construction erosion and storm water control plan and a drainage plan for the project operation phase. These plans would ensure the use of appropriate erosion control best management practices (BMPs) during the construction period, including, but not limited to, development of construction access road, use of filter fences, straw bales and temporary sedimentation ponds, and permanent stabilization upon completion of construction. All impervious surfaces will discharge to and through a proposed stormwater management facility that is consistent with the engineered stormwater control plan. . Furthermore, stormwater from roadways, building and parking areas, and other related aspects of the proposed facility will be tied back into the currently existing adjacent stormwater management facilities with no additional adverse impacts. No additional mitigation measures would be needed. Therefore, utilizing these best management practices, erosion and other stormwater-related impacts during construction and operation of the project are not expected to be significant. The GeoEngineers geotechnical engineering report (2007) concluded that the Project “may be developed satisfactorily as planned with respect to geotechnical issues,� provided that
USIT BOW HILL EA
August 20, 2010 DRAFT