2207 GIBSON PL 2022-10-28 - Laserfiche WebLink

at the toe of the slope north of this project and eventually into Puget Sound via a ditch along the south side of the BNRR R/W and then a large diameter culvert to the west. During the site visit there were no signs of flooding or capacity issues within the observed downstream systems. 2. EXISTING CONDITIONS SUMMARY The site covers approximately 0.59 acres. The proposed disturbance area of the existing site has not changed notably since 2017 and consists of a SFR, concrete & asphalt driveway, flat landscaping. Therefore, the addition of some new driveway and the garage roof area will be considered new. This project proposes to increase the on-site impervious surfaces by approximately 2,702 sf(0.06 Ac) over the current conditions, as permitted under the previous SFR building permit. This project does not propose any clearing or grading within the steep slopes north of the project parcel. The overall slope of the lot is from south to north. The proposed disturbance area averages less than 3% and the steep slopes north of the proejct are greater than 40%. 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. Langus Garage 15-0403-L March,2022 Page 4