Background Federal Aviation Administration (FAA) design standards require a 1,000-foot runway object-free area and runway safety area (RSA) beyond the ends of each runway. To meet the FAA requirements, approximately 6.19 acres of wetlands (4.65 acres of jurisdictional wetlands) at Hillsboro Airport were impacted as a result of filling activities and the relocation of NW Evergreen Road. Proposed mitigation for the unavoidable impacts to wetlands consisted of on-site creation of a new drainage channel to mitigate for 0.27 acre of impacts and off-site enhancement, restoration and creation on the Randall site to mitigate for wetland loss. The Randall site comprises 22.3 acres located on both sides of NW 334th Avenue in Hillsboro. At the time of purchase in March 2001, the property comprised open fields that had been used as pasture for several decades, residential structures, a cattle pond drainage swale and native deciduous forest. Site preparation included the removal of all structures on the site, the abandonment of two water wells and the installation of 11 groundwater monitoring piezometers.
Mitigation Plan The goal of the proposed mitigation is to restore and enhance wetland and riparian conditions in order to replace wetland functions and values lost as a result of the RSA expansion. The mitigation plan provides for 6.68 acres of enhanced wetland, 3.32 acres of created wetland and 1.82 acres of restored wetland area, for a total of 6.25 acres of wetland mitigation credit to compensate for the loss of 5.92 acres of wetlands. The objectives of the plan include restoring wetland hydrology, creating wetland forest and scrub/shrub habitat, enhancing wetland prairie and riparian areas along Dairy Creek, and enhancing and restoring upland habitat.
Status Excavation and grading of the site was completed in November 2002 and planting was completed in March 2003. However, in 2006 Port mitigation staff identified a 1.4 acre wetland shortage that will be corrected in the fall of 2007. The wetland shortfall and subsequent correction will result in additional monitoring years to ensure the success and survival of plantings in the regraded area.