1632 46TH ST SE 2020-06-18 - Laserfiche WebLink

Central Park SFR-CAR&Mitigation Plan The following sections provide an outline of identified critical area impacts and proposed mitigation measures intended to off-set these impacts. All critical area, impact, and mitigation areas are found in Appendix B. 4.1 Proposed Impacts The proposed project has minimized critical area impacts to the greatest extent practicable. The house design and placement has been sized and oriented on the site to minimize encroachment into the buffer. A total of 1,670 SF of buffer area will be permanently impacted to allow for the construction of a new single family home. The impact areas is dominated by Himalayan blackberry, bindweed,and Japanese knotweed. Additionally,the project has proposed 303 SF of temporary buffer impact and 391 SF of temporary wetland impact to allow for the installation of a stormwater conveyance and dispersion system. The location of the stormwater infrastructure is influenced by the existing topography found on the site. Instead of discharging water at the top of the slope,a conveyance line has been proposed to pipe water over the slope and discharge into the wetland. This will help preserve existing slope stability and provide wetland recharge to an isolated wetland. The proposed project should not result in a discernible cumulative impact to wetland or buffer areas. The adjacent properties have been previously developed with single family residences and the paved pedestrian path. The proposed enhancement outlined in the following section will result in an increase in local functions and values as a result of the proposed project. 4.2 Proposed Mitigation Measures All temporarily impacted areas will be fully restored by removing any existing invasive vegetation and installing native trees and shrubs. The proposed permanent buffer impacts associated with this project will be mitigated for through the enhancement of the remaining buffer area on-site or 3,858 SF. This will include removal of existing invasive vegetation and garbage/debris and installation of native trees and shrubs. More specifically,the following efforts are proposed: 1. Invasive plants (predominantly Himalayan Blackberry)will be removed from the on-site buffer area. •I 2. Jute matting will be placed throughout the area where invasive plants are removed to prevent erosion. 3. Native trees and shrubs will be planted throughout the buffer area. 4. An erosion control seed mix will be applied to the on-site buffer area to reduce future erosion risk. 5. A split-rail fence and appropriate signage will be installed along the on-site buffer edge. Table 2: Mitigation plant list and spacing requirements Common Name Scientific Name Spacing Quantity Western Red Cedar Thuja plicata 10 to 15-feet on center 15 Big leaf maple Acer macrophyllum 10 to 15-feet on center 15 Salmonberry Rubus spectabilis 3 to 5-feet on center 35 ; Snowberry Cornus sericea 3 to 5-feet on center 25 Sept`r-nrl;'i.7.201C PAT 9 p<>rc_i ti b.iPi<;n;:L.... 6