2211 GIBSON PL 2023-04-10 - Laserfiche WebLink

, 2. EXISTING CONDITIONS SUMMARY The site covers approximately 0.86 acres. The proposed disturbance area of the existing site has not changed notably since 1997 and consists of a SFR, detached garage, shed, asphalt driveway, flat landscaping and steep forested slopes. The existing SFR has been removed from the site and the existing driveway will be modified with some of the existing driveway surface receiving an overlay in the area of the access and some being removed. Therefore, the overlay of the existing driveway is not considered a replaced surface and all of the remaining proposed impervious surfaces will be considered new. The proposed improvements for this project include the removal of the remaining garage and shed, construction of a new house and driveway additions to serve the project. This project proposes to increase the on-site impervious surfaces by approximately 6,674 sf(0.15 Ac) over the current conditions, i.e. excluding the SFR already removed. This project does not propose any clearing or grading within the steep slopes of the project parcel. The overall slope of the lot is down and to the north. The proposed disturbance area averages less than 5% and the steep slopes are greater than 40%. The existing roadway Gibson PI., is able to sheet flow runoff onto the project site. This runoff is immediately collected by landscape flower beds and is not expected effect the project area. This project will not affect any offsite flows from passing through or around the site as in the existing conditions. All runoff from the proposed developed hard surfaces on this site will be collected and conveyed to the toe of the bluff to the north via an 8" conveyance system with diffuser tee installed as part of the adjacent short plat to the east. The discharge location will be on the south side of the BNSF railroad with Puget Sound located to the north. Therefore, the runoff will be discharged at a location where it will flow through the existing ditch system for the railroad and then through an existing culvert into Puget Sound which will have negligible impact on the downstream existing conditions. Based on the existing soil information and the setbacks of the proposed improvements from any of the property lines or critical areas there is little potential for erosion or sedimentation during construction, assuming the basic BMPs included in the SWPPP are installed and maintained properly. Refer to Figure 2 for an existing basin map. Robinett SFR 15-0403 Revised:July,2016 Page 4